Like a toolkit for your website?
I think every developer/designer has something like that. I, personally, keep my resources in a massive, 4GB folder (I think?) on my desktop. It's always useful to have when I make that. Something like that?
As for making it, I would sit down for a day and just start getting stuff - make sure you know the license and include it in the same location as whatever you might use. For instance, I downloaded tons of Social Media Icon Sets one day. I have the license in the folder of the set so that I can know the license in 4 years, if need be (if it doesn't change).
After you've got a base set, just keep adding to it. I subscribe to a few RSS feeds that give out some nice giveaways - if I see a nice brush set, or texture pack, I'll download it and add it to my collection. That way, I can always have those tools on hand.