First, let's start with tools. Not only are they durable, they're also easy to find at yard sales. instead of spending $10 on a new hammer, you could find a used one for a buck. Just be sure to stick to the simple stuff. Anything with a motor can wear out quickly, so only buy power tools from someone you trust.
Next, if you or your children are trying a sport for the first time, check out a garage sale before springing for a new pair of skis or a tennis racquet that you might not use a lot. The same goes for weights and other basic exercise equipment. Most of these items are sturdy and built to last. Just be careful with electronic gym equipment, like treadmills. They can be great bargains, but you should inspect them very closely before deciding to buy one that's used.
When it comes to furniture, wood is definitely the way to go. It's easy to clean, plus you can sand it, paint it and decorate it to give it your own unique look. Not only will you be saving money, but there's a good chance that an older piece of wooden furniture is built better than what you'll find in a store. Stay away from mattresses and anything with upholstery, though. Not only are they tough to clean, they might carry bed bugs as well.
Musical instruments.. Your child is entering the musical part of their schooling. You need a trumpet, trombone, flute, etc.. look for them used or to rent first. But, do NOT get tied into a contract when renting. Your child may decide that this instrument is NOT for them.
Finally, if you or your kids love to read, buying new books all the time can add up. Unless you're planning on building a library, save money by buying used books at yard sales. You can also go online and find lots of websites that sell secondhand books in good condition for cheap. When you're finished reading, you can list them yourself to recoup some of your expenses.
Before you buy something brand new, remember these tips to avoid overspending. If you know what to look for, you can find hand-me-downs that are just as good as new and cost just a fraction of the price.