1) Wash and save plastic butter tubs, large yogurt containers, coffee cans and the like. They are great for sending home leftovers with your dinner guests, decorating with wrapping paper for holiday cookie giving, or a homemade drumset for your toddler.
2) Keep old egg cartons to use as paint "palettes" for kids craft projects.
3) Wash and snip up leftover fresh herbs before they go bad. Put about a tablespoon into an ice cube tray and fill with a tiny bit of water. Freeze overnight. Pop out the cubes and store in a plastic baggie in the freezer. It's great for when you need a bit of parsley, basil or cilantro for a recipe!
5) Also a good use for ice cube trays: pour in the old coffee left on the pot that you didn't drink. They make yummy ice cubes for making your own iced coffees the next day.
6) Small cookie cutters are excellent for fun with Play-Doh as well as make perfect stencils for art projects.
7) Invest in a pair of kitchen shears. I use these things for everything, from opening packages to trimming fresh flower bouquets to cutting up pizza into bite-sized pieces for Alice.
8) Save the small clean brown paper sacks that fast food restaurants always give too many of. They are great for packing work or school lunches in later.
9) Another easy way to save fruits and vegetables that are getting too ripe or about to go bad is to dehydrate them. Slice up the apples you didn't get to eating or the abundance of tomatoes from your end of the season garden harvest. They make delicious dried snacks.
10) Use cloth napkins. I find sets at thrift stores or garage sales and keep a basket on my table of mis-matched ones for everyday use. They are also super easy to make out of scrap fabric and make great gifts. It's also way more eco-friendly than the paper ones.
These are just some of these hacks I've stolen from others (like this fantastic website of tips from parents, learned from friends or discovered myself. As always, I'm up for tricks or thrifty ideas to save money, time, and resources.