Probably the dreamcatcher he got Dream to charm, for Mithos! 'cause MITHOS IS TOTALLY COMING HOME ALIVE :T and might need it, plus it's actually useful. If he hadn't given Cheshire the jar of sunlight it also might've been that, just because that was super neat. His Sterling key would also be a contender out of nostalgia reasons.

Will KK use her phenomenal cosmic powers to try to figure out ways to visit people after she goes home? Or ask 'Kady to?