So if it were me, I'd tip the caterer, and any waitstaff, and the bartender each individually. The handshake tip comes in quite handy for a situation like this. This also allows you the opportunity to verbally thank each person.
I agree with tipping waitstaff/bartender individually. I like WillyNilly's approach and agree that it allows you to verbally thank each person. I think this is a nice touch.
Silly question -- would you, then, need to tip the caterer? Isn't that akin to tipping the owner of a beauty salon?
Not silly at all, its an excellent question.
And the answer is, there is no need to tip the caterer if they own the business. But I would anyway, because I tip all service people* and especially because I would feel so super weird awkward tipping some of the hired help but not all of the hired help; so if I was tipping the waitstaff & bartender, I would feel odd leaving the one person who pulled it all together for me out.
* My general stance is I tip on luxuries - so if I could do it myself but choose not to because I'd rather pay, I tip. So food service, nails, hair cuts, movers, the laundromat wash-n-fold person, etc I tip because i can do all those things myself, I just don't want to. I don't tip my Dr or my car mechanic or the help desk folks at Staples, because I see those as professional services not luxury services.