for people who also have a mild impulse shopping problem, I've found it useful to identify the itch I want to scratch: is it spending money or is it getting things? If it's spending money, I trick my brain by paying off something I owe. Like a few years back when I was feeling dangerously shoppy, I would drop a big chunk of change as a student loan payment. When I was buying an entire new mouth of teeth, I'd transfer money from my checking to my secret ultra hard to access tooth account.
If paying myself or paying a debt doesn't work, I find a charity or gofundme that's worth supporting. (You gotta be careful with that last one, it's really easy to be spend way more than you should, budget-wise, because it makes spending money feel good morally, which can be an incentive to keep going.) I also like to keep cash on hand so if I see someone who needs money, I can give it to them. It's a financial decision made impulsively for an opportunity I won't get again (giving $20 to this exact person at this moment of need). All this soothes the spending beast inside of me, and I don't deal with the Money Shame that comes with $100 of amazon orders.
If I want to acquire things, I download a lot of research articles I know I probably won't read, or I get an enormous stack of books from the library that would be impossible to finish before I have to return them, or I'll download a bunch of albums I tell myself I'll get to someday. Sometimes it's enough to just make a list of things of things I want to do or own. A list of one hundred movies I've curated from best of lists that in this moment I feel motivated to watch. Add tv shows to my watch list on netflix. Add fics to my "to read" list on ao3. Anything that feels like I'm adding to a hoard.
If I still want to shop, well, I'm probably gonna spend more money than I mean to, but I at least make sure I'm deliberate about my spending. If I'm gonna blow my cash on something, it should at least be worth it. That means either very cool or very useful. And honestly, the things you tell yourself are useful while in the shopping haze are never that useful, so you might as well go for very cool.
This is all to say I fell into a trance last night and this morning woke to receipts and tracking info from etsy dot com. And I am like "yikes." But I did get something that is so so so stupid that I can't wait to show it to you all when it arrives.