If I was going to do this and wanted a liquid developer, I'd use Rodinal. I'd carry a bottle of TF-4 fixer as well - this cuts down on the other chemistry somewhat by eliminating stop bath and hypo-clear. But, caffenol is not a bad idea, the easy-to-find ingredients aren't likely to set off any false alarms with hotel staff. Film developing equipment might seem a little "funny-looking" to the uninitiated, so I would keep it in my luggage when not in use, just to avoid any unexpected conversations with the local authorities.
Hate to sound all paranoid about it. :/