This is to serve as a starting off point for what to look for when you are out at a thrift store, garage sale, etc. This list is very general, but we will take be taking deeper dives on most of the items on these lists.
I spend a lot of time on different Facebook groups to find out what people are finding and what they're looking for. It's free and easy research, in my opinion. I've definitely been alerted to brands or specific things that I wouldn't have thought of or have heard of, then when I'm out sourcing, I have even more knowledge of what to pick up and what to leave behind.
There is a virtually endless list of things to look for when starting out. I stick with clothes, especially vintage, for my reselling venture for the most part, but have recently gotten back into sourcing hard goods, but doing as much research as possible before actually buying something. I am also still selling my comic books, toys, and collectibles.
Of course the bottom line to all of this reselling business is buy low, sell high. You definitely want to source your stuff for as low as possible and try to sell for as high as possible. It won't always work out that way and you may find yourself selling something for somewhere in the middle of low & high or hopefully infrequently at a break even.
You'll definitely want to make sure whatever you're picking up to resell is in good condition, depending on what the item is it should be:
Always do research before you go out sourcing and while you're out. Check sold comps. Make sure what you're about to buy can turn a profit. There are of course no guarantees that your item will sell quickly, or at all in rare instances, but being armed with as much information as possible is your best bet to making "easy money".
Below are some more experts in the field echoing what has been mentioned here: