Good discussion. I usually keep 1s, 5s, and 10's in a ziplock bag onboard. A friend's son works at a marina here and makes a LOT of money due to tips in the summer. Much more than his peers make at other part-time jobs, so it's not like they rely on it like waiters do. They have to at least be paid minimum wage. Still I'm happy to tip them and also gas docks and especially pumpout boats. Minimum is usually $5 pp. Many are college kids working for the summer so a good cause.
So here's my mini-rant on tipping in general. Where does "it's their job" end and tipping begin. We all know to tip waiters and bartenders but what about mailmen, garbagemen, plumbers, painters, landscapers, etc, etc. Personally, if I hire someone and they do a great job, I'll round up and include a tip. Here's a pet peeve of mine. You wouldn't think of not tipping a bartender who spends 30 seconds pouring draft beer into a glass. Somehow, that's worth a buck or 2 on top of the very expensive price. Why is that expected/accepted, but very few people tip the housekeeping service at a hotel? I try to leave some cash when I can, but don't often carry any/much. I would be fine if the hotel bill had a line for adding a gratuity like a restaurant does. Compared to the beer bartender, here is someone that might spend an hour or more cleaning up after you and if they are lucky they may get a couple extra bucks. It could be a $600 bill for a few nights and they usually get zero. I travel a lot for business so maybe I'm extra sensitive to this, but even our corporate policy only allows a couple dollars per day for gratutity. These are some of the hardest working and overlooked workers who really are performing a service and are deserving and in need of tips more so than the smug bartender pouring your $10 beer.
Carry on....