A dollar for the driver (at least, as an FO). Maids? Never stayed at a hotel long enough to require fresh towels and such. And even during training, you should tip the driver if they take you somewhere.

I was actually thinking about the total cost of tips over the course of a year and it adds up like this:

$6.00/trip (1+2+2+1)[Day 1+2+3+4]
$30.00/month (5 trips a month x $6.00)
$360.00/year (12 months in the year)

Kind of expensive if you're on first year FO pay at a Regional. But it keeps the van drivers happy and it's probably not going to break the bank. Plus, I would think you could deduct it from taxes at the end of the year.