First I took care of all of my "need" list purchases.

Then I took care of all of my "want" list purchases.

Then I added a handful of "dang I shouldn't have tried that because now I like it and need more" purchases.

Lastly I tried to make a list of anything else I should get and 24 hours later my list was still empty

That's when I knew I was done.
In early 2013, I started stocking up on nic and RBAs. I had been DIYing since early 2011, but had never built a coil. I stocked up on RBAs anyway, just in case.
I first started stocking mech mods, starting with my first REO in March 2014.
I didn't start stocking up on VV mods until October 2014. That's when I bought my first used Provari. I had only had a couple of VV mods before that and was very dissatisfied with their quality (or rather lack of quality). It was time to find something that would last and last and last.
If I hadn't started so far ahead, there's no way I'ld be ready now. I have no credit cards and make very little money. I was even unemployed for several months because of health issues.
I would really like more time to experiment. I'm so very slow to try new things.
For example, I was thinking of trying the Kayfun Mini V3 and the Tilemahos. I hesitate to try new RBAs because most people recommend RBAs that are too airy or too hard to build for me.
I guess I really don't need anything else. It would just be nice to try some things while I still can.