I keep lots of lists--lists of things I need to do, grocery shopping lists so I don't forget a crucial part of a meal, a list of appointments and meetings I can't miss, and a "to buy" list where I write down all of the things I want to buy that aren't so critical that I need to run out and get it now.
So far this year I have pretty much stuck to my no-spend goal for this year. We haven't traveled anywhere since the beginning of the year, if there is something I want I try to find it at the Goodwill first, and I have bought exactly one thing online so far this year (a half-off day pack from REI). So far so good.
But there are still several things I want to buy yet don't absolutely have to have. I would like a waffle maker but haven't been able to find one at the Goodwill yet (the ones I've seen there were pretty cruddy), and I would also like an air popper (I currently make popcorn the old fashioned way with a deep, heavy pan on the stove...it works). I have a Dell XPS 13" laptop which I have been using for four years that I would like to replace with a new version but the laptop still works perfectly so this isn't a critical need (I had bought a 15" laptop for home use but rarely used it and got tired of transferring files back and forth so it went back to the store).
Other things on the list that I would like to have include a new tile floor in the house, all new appliances, a dash cam for hubby's van which we rarely ever drive... Eventually some of the things on the list fall off when I realize I don't really want the item any more and since the list is prioritized (most wanted things at the top of the list), things may move up and down the list by order of importance so stuff at the bottom of the list are probably things I don't really want or need.
I think keeping this sort of list is a good way to determine if something is just a passing fancy or something that is really really wanted. It also keeps the items top of mind so that if a super great sale comes up I will know that I have been looking for the item for a while and be able to determine if the sale price is really great or just OK. It also seems to keep me from buying things as I know that I can eventually get the items but don't need it right now so it can just hang out on the list until I have the cash to get it. List psychology...it works!