It's a pretty simple idea, but it's surprising how little it occurs to CalTrain riders to do it, or to transit agencies to encourage it.
I got my schedules mixed up today, and was standing on the SB platform at Menlo Park this morning at 10:35, and it slowly dawned on me that there's an 8:35 and a 9:35, but no 10:35--the next train wasn't til 11:00.
So I set off by bike in the general direction of work, got to Palo Alto, and it occurred to me to try the VTA's 522 Rapid, which goes all the way down El Camino (then swings east across San Jose), the same route as the 22, but with fewer stops, and busses equipped to get traffic signal priority.
I have a two-zone CalTrain pass, which lets me ride VTA and SamTrans busses free.

My bus was actually a regular bus in the VTA's usual paint job.
My bus left at 10:54. I got to work at 11:30, and that 0:36 included a stop to pick up a Nicoise salad at the Mountain View Trader Joe's. So the overall trip time is pretty good compared with my estimated arrival of ~11:20 had I waited around for the train.
Now I admit that the bus alternative may not appeal much to hotshot dot-com commuters who ride CalTrain from Portrero Hill down to jobs in Mountain View, but I think there's a lot of other travel patterns where if people were more aware the busses that VTA and SamTrans run up and down El Camino, and thought of them as a complementary service to CalTrain, in more or less the same corridor--instead of just "welfare transit for people who don't have cars", they might actually give them a try. For weekend outings up and down the peninsula, for example, timing the start of a trip to hit one of CalTrain's hourly runs is not so bad, but having to check your watch and make sure to punctually leave whatever leisure activity you're pursing to get home is annoying. Why not take the train there and the bus back? Or if one of CalTrain's "unfortunate incidents" interrupts your evening commute, and your trip isn't too long, why not head over to a bus stop? It might be quicker than waiting three hours while the emergency response folks hold up the line writing reports and cleaning up.
Transit agencies could do a lot to encourage this sort of thinking just by actually letting riders know it's possible. Somewhere on their schedule, CalTrain should at least mention what busses complement their service, and mention the "two-zone pass = bus pass" perk a bit more prominently. It would also be nice to expand the priviledge to regular tickets, or even, to accept local agencies' passes within their jurisdiction.
All of these agencies do belong to us, after all--it shouldn't be too much to ask that they work together!