1) Lotions and Potions - purchased a body lotion with lovely fragrance but found out at home that if you use it all over - it's kinda strong? Mix with a fragrance free body lotion and voila! Or just add a few drops of perfume to the fragrance free stuff.
2) What to do with used vegetable cooking oil? Its very unhealthy to re-use cooking oil more than a few times. Aside from storing it for later use as lamp oil, hot oil makes a great de-greaser. If you have greasy pot lids, brush on some hot oil until the grease spots run off. You can then clean the lid and it will be grease free. This works with bacon or Crisco too but it's harder to clean this if the oil congeals.
3) Old socks especially the very stretchy sports socks or the ones the airlines offer - these are excellent shoe covers. Keeps the dust off and keeps your shoes away from your clean cloths in the suitcase.
4) Old "Cafe Steamers" plastic containers - What can't you do with this one! The two piece container with the perforated insert makes soap dishs, drains nicely for plants and anything else. Reuse as a draining system for single servings of pasta, or add water to the bottom to microwave food without getting it soggy.
5) Those little shampoo bottles from hotels or plastic bottles from prescriptions, etc... - fill again with shampoo or other personal supplies. The most obvious use is travel but the real deal is the home emergency kit. You need 3-14 days worth of supplies for everyone in the family. Don't forget to jot down the expiration date. You can also put together personal pharmacy kits with small amounts of useful OTC products. It can save you money and your day if you've got something for whatever ails you on hand.
6) The tough, clear plastic bags with snaps or zippers - I find many pillow cases and sheets are packaged in these. Obviously these are always useful. Small ones are useful for creating kits (first aid, cosmetics) for travel. Larger ones are useful to holding dirty laundry in your luggage. Use as a dustcover. Got equipment to grommet handles onto these bags? Great totes.
7) Old sheets - if you sew, what can't you do with this? If you can't sew, try fabric glue. How about laundry bags for your delicates? Toss delicates and sweaters straight into the washing machine. As long as the dye can tolerate this treatment, the fabric will be fine. You will remember to use the front-loader with the delicate cycle for your woolens right?
8) Old shoelaces especially from sports shoes - These are just about the toughest cord I've ever encountered. I've used this repair a salad spinner (the kind where you pull on the cord and it spins), used these to replace drawstrings in sweatpants, laundry bags, the list goes on.
9) Filters for air purifiers - vacuum gently to renew. Even better, layer cheesecloth on the filter when it's new. When the cheesecloth looks like the lint filter in your dryer, throw this away (or look up suggestions for how to use dryer lint - just be sure you aren't allergic to this stuff). Generally, extends the life of your filter by a year.
10) Lemon or orange peels - zest it first thing. Dry the zest and it'll last for months in that old spice bottle you're reusing right? No need to purchase lemon/orange peel. Hint, drying goes faster if you use the leftover heat from your toaster/oven. Don't overheat. It's supposed to be slow and gentle.
11) Feel the need to stock up on crushed red pepper flakes, chili oil and whole red peppers for stewing? Notice it fades before you can use it all? For most people, it's all the same red chili. You can't taste the difference between the Facing Heaven chili's vs. the Tien Tsin vs. the Dundicut's can you? (Can you? You have my respect) Buy a bag of the whole stuff. Drop whole or crushed peppers into oil to make your own. You can use a blender or a mortar & pestle to crush the peppers.