I often do travel with just a couple of primes (though I haven't done so with my Canon digital gear yet, as I haven't had it very long), and my usual combo is a 28 and a 50 (on FF/35mm film). I'm not one for long lenses, so 135, 70-200, etc don't really interest me.
I'd tend not to go for L lenses (and I know there isn't a 28L anyway), because when I'm traveling I value small size and low weight. My only Canon primes at the moment, in fact, are a 50/1.4 and a 28/1.8, because those are the two FLs that I really can't manage without.
I do occasionally travel with a 35 and a 50, or even a 35 alone, and sometimes I'll add an 85 to the mix - it depends on where I'm going and what I expect to be shooting. I expect I'll add an 85/1.8 to my Canon gear before too long (but there's no 35 to suit me - I don't want the 35L, because it's too big, and too expensive for me, and I don't like the bottom range plastic non-USM lenses).
Best,
