What can I invest in with my excess of Caps?

After a few lucky nights gambling on the Strip, a successful raid on a mysterious vault, and a smattering of snow globes my Courier has acquired an excess of 100,000 bottle caps. Now that I have all of this money what can I do with it?

I had spent a few thousand caps on implants to upgrade my character, as well as purchasing all of the upgrades in the Lucky 38 Presidential Suite but I still have more caps than I know how to spend. Weapons, especially from the Gun Runners Arsenal, seem like a decent investment but most of them will end up stored in a box somewhere because I don’t need that many, especially after purchasing Medicine Stick.

Are there any other money sinks in the Mojave that I can upgrade? I’d prefer purchases that offer permanent upgrades rather than buying weapons, equipment, or consumables – things I can scavenge on my own.

This question can be extended to purchases in any of the game’s DLC.