I initally went for the catagories that interested me, and then I checked out completed listings (under advanced search), other ideas came up when I needed stuff myself and purchased them, alot of my lines are things that happened that way. Ideas are easy, the real hard work came up for me when I tried to get good suppliers and MOQs.
If your out and about on your daily routine and spot a bargain.... grab it.
I spot bargains on the reduced shelf in shops... good brands just old stock the shop needs to get rid of to make space for new stuff - add a few quid
(or dollar as in your case) to the price you paid and you buyers still get a bargain and you make a couple of bucks (or pound shillings if in uk)
Its not the biggest money maker but its a little extra and something to do if your bored and its not vero
Buy stuff in sales and put it on.... you'll be suprised.... people will always buy
Whatever you choose.... make sure you have fun xXx