Vinyl? Comic books? Tiny porcelain babies? Forget that! You're gonna be a RAIN COLLECTOR!
The way to be a collector is to get in on the ground floor and sell at the peak. Those guys who bought Action Comics 1 on the stands and then sold it in 1998 made SO MUCH MONEY, didn't they? So the trick is to figure out the next thing people will want to collect, and be ready to sell to them when they figure it out.
We say the next big thing is going to be... water. So get yourself a rain barrel and let it fill up to the brim. Maybe from time to time use it to water plants or something just to keep the water in mint condition. But keep that water. Keep it safe. And then, when the big water collectors boom of 2187 happens, you'll be at the forefront with pristine stock the collector will value.
Then your only problem will be if you sell at the top of the first bubble or if you wait until they release Water II: Age Of Wetron.