My kitty seems to have swallowed a string or something

[Der Blaue Engel]

He's been making occasional gagging faces since yesterday and spitting up a bit of clear fluid. I couldn't figure out what he was doing; at first I just thought he was being weird (because he frequently is, and both my cats puke with the usual cat frequency). Tonight when I got home from work, he seemed a bit listless and I noticed he hadn't eaten his food. A little while later, he came into the bedroom doing the gaggy thing again and spit out a piece of unchewed food, and it finally dawned on me that he must have some kind of obstruction. :(

He doesn't seem to be having any trouble breathing. Am I being stupid to wait until morning to take him to the vet?