This question was posted on a discussion board recently.  Not only do I reuse many physical objects, but I can reuse the list I made for that discussion as an article on my own Website! 

First of all, I want to rave a moment about how glass jars are much better for food storage than plastic containers! We save the jars from peanut butter, salsa, spaghetti sauce, etc., and use them over and over again. They wash so much cleaner so much more easily than plastic, especially with greasy or sticky foods. Things seem to stay fresh longer in glass. The threaded lids almost never leak. My very favorite feature is this: If you put something hot in a glass jar and fill it very full and put on the lid immediately, sometimes it will seal so well that the food stays good (in the back of the fridge) for a couple of months. I'm talking about the jars from spaghetti sauce and such that have a circle that pops up when you break the seal—you can get that circle to pop down again when the jar is full of hot food. I wonder if it's then shelf-stable, like the original food was until opened, and doesn't even need to be refrigerated, but so far I haven't been brave enough to experiment! I love spaghetti and enjoy making my own sauce, but I figure I may as well make a big batch while I'm at it, so keeping it from getting moldy before we use it is an issue.

Glass juice bottles are wonderful, too. I snagged 7 of them during my big recycling project in 2002, and I'm still using them daily for juice to drink with my lunch at work.  Refilling them from a half-gallon pitcher mixed up from concentrate at home costs less than half as much as buying new single-serving bottles of juice.

We reuse various types of food containers to buy food from the bulk section of our co-op (you scoop from a bin into your container, after weighing it empty and writing its weight on the label so the cashier can subtract it and charge you only for the food). It's fun deciding what's the best container for which food. There are products we haven't bought in years whose containers we're still using: raisins in a Maxwell House instant coffee jar, oats in the huge plastic jar that held 4 pounds of generic peanut butter, etc.

I cut up old cotton knit clothes to make hankies. Last time, I was left with some shreds of pretty fabric from the edges, so I used them as cushioning for a gift I was mailing to my mom—rather than wrap it, I just put it in an envelope and stuffed the gaps with the fabric scraps.

Old pantyhose make great lint filters for the washing machine: Just slip one leg over the end of the drain hose and tie it into place.  They're also good for storing onions: Put an onion in the foot, tie a knot above it, put in another onion, tie a knot, and so on until you have a chain of onions you can hang from a hook. Being separated helps to keep the onions from spoiling.

Our household hints page includes ideas for reusing mesh produce bags, remnants of bar soap, extra address labels and other stickers, scrap paper, egg cartons, and unwanted tobacco.

We made our own Christmas tree out of a cardboard box and the green plastic bags the Sunday paper comes in.

We save gift wrap and ribbons to use over again.

When Nicholas was a baby, he had hours of fun playing with shaker-toys made from the cardboard canisters with plastic lids that some foods come in, with a bottle cap or something like that inside.

My Girl Scouts designed a restaurant as part of their Cooking badge and held a "grand opening" where we served "free samples" of the foods we'd made. All the dishes we used were food packaging the girls and I had saved, which would otherwise have been recycled or trashed, and which got this one additional use before it met that fate. It was fun seeing the variety of dishes we collected and deciding which was best for what food!

I save business reply mail envelopes that I'm not going to use, and I give one to each Girl Scout patrol (small group within the troop) to collect their dues money. Each girl writes on the envelope her name and how much she paid. That way I just toss the sealed envelopes into my bag and don't have to count the money until I get home!

The thin cardboard boxes from cereal and other foods are great material for making name tags.  I like to start the first Girl Scout meeting of the year by setting out some boxes, scissors, a hole-puncher, a ball of string, and markers, and telling the girls, "Make name tags."  They figure it out and feel pretty clever!

When we moved, I bought new pink dishcloths to match our new kitchen and demoted the old ones (green and other colors) to bathroom cleaning cloths. As they get worn out, they become "rags" that get one last use for some yucky job and then get thrown away.

We use produce bags over and over again until they tear or something gets moldy in them. After using the produce, we put the bag into one of our canvas tote bags that we use for grocery shopping so that we'll take it back to the store next time.

We use bags from bread, etc., to store various foods and just keep shaking out crumbs, rinsing or washing if necessary, and using them again.

Family-size yogurt tubs have a bunch of uses: buckets for outdoor play, temporary plant pots, bath toys, diluting the vinegar to wash my hair, soaking cloth pads or bloodstained hankies in cold water, soaking other stained items in Oxi-Clean, mixing up wonder-cleaner, rinsing the bathtub after scrubbing.... We keep a yogurt tub next to the sink as the compost bucket (temporary storage of food scraps destined for outdoor compost bins) and keep washing and reusing it until something gets really yucky in it or it's stained by coffee grounds, and then it gets recycled.

We save take-out soup containers, similar to yogurt tubs but clear, to bring home leftovers from restaurants. In a pinch, we use yogurt tubs for that purpose and tape on a label to show it's not yogurt in the fridge.

We prefer paper milk cartons to plastic jugs because the milk tastes better and we've read that milk in an opaque container retains more nutrition. After finishing the milk, we rinse the carton, open the top all the way, and set it on the floor next to the kitchen trash. Non-compostable food scraps go in there, and the carton then gets folded shut so the food won't leak into the trash bag and make a mess when the trash is carried out.

I've made some unique fridge magnets by cutting amusing panels from comic strips and gluing them to magnets. There are two ways to do it:

1. Take a flexible magnet with an ad on it, which is at least as big as your cartoon. Remove (or at least degloss) the ad with nail polish remover. Let dry. Use white glue to stick cartoon to magnet. Let dry. Cut off any excess magnet. Coat top surface with clear nail polish. This whole process will go more smoothly if you happen to have an old cookie sheet or other flat metal surface to which you can stick the magnets to keep them flat while you're applying stuff to them and letting them dry.
2. Glue cartoon to thin cardboard from a cereal box or clothing package. Let dry. Coat top surface with clear nail polish. Hot-glue or rubber-cement back of cardboard to a small round or bar magnet.

Use the pictures from old/unwanted calendars as art to hang on your walls.  If you're not going to frame them, use an X-Acto knife and ruler to cut them from the binding so the cut edge is nice and straight.  This was my main source of home decor when I was in college, but I forgot to include this tip until I saw it on another site! Here's Kara's article with nice example photos.

Here are some links to other people's creative reusing ideas (I add to this frequently—check back!):
Turn plastic shopping bags into yarn for craft projects!
Turn an old coat into teddy bears.
Make paper mache out of cardboard egg cartons.
Ten different ideas for glass jars.
Polystyrene (#6 plastic) containers from fresh produce, take-out salads, etc. can be used for shrink-plastic art.
The tin from Starbucks mints is exactly the right size to hold cotton swabs.
Use an old cereal box to make a tray for transporting and serving baked goods.
Use an old plastic bottle to make a scoop or luggage tags.
Turn an old oatmeal box into attractive storage for extra toilet-paper rolls.
Lots of uses for plastic cereal box liners.
Use the zippered clear vinyl bags from bedding to store games whose boxes have been damaged.
Use the silverware caddy from an old dishwasher to organize desk supplies, and use cardboard corner reinforcements from an appliance box to make a book rack.
Make a gift bow from a magazine page.
Many uses for junk mail.
Turn a stained T-shirt into a pretty outer layer.
Use a depleted gift card as a dish scraper.
Make an old dress shirt into cloth napkins.
Make old pillowcases into boxer shorts.
Make a pair of adult jeans into adult shorts plus two little-girl skirts.
Lots of uses for empty food canisters.

Click the "reusing" tag at the bottom of the page for more Earthling's Handbook articles about reusing things.