Most will take a 5 year vacation.
Just about everyone I know would start a business, volunteer, do creative things, contribute to making the world a better place.
But, at the end of the day, I don't care how people spend their time or their money. If some fraction of the population wanted to bum around on their minimal UBI for the rest of their lives, fine by me. It's never going to lead to a life of luxury, and I quite honestly don't care if that's how they want to waste their lives.
Funding my fellow countrymen who want to squander their lives, so long as they're doing so peacefully and in the privacy of their own homes? Sign. me. up.