Room service: Depends - these days a lot of US hotels charge for delivery/service etc. so it seems preposterous to tip on top of that. If there's no extra charges then I will tip. I will also mention that I think room service prices are often absurdly high and if they were more reasonable I'd order room service more often.

Bags: Yes for tipping when I get help although when I'm alone with my rollaboard I don't need or want the bellman

Maids: Typically don't tip unless I make a real mess in the room

One area not mentioned here where I do tip is if I call down to ask for something extra to be brought up to the room like extra pillows, or extra towels or a rollaway bed etc. Those sorts of things were a small part of my job description when I worked at a fancy hotel in college ("houseman" was my title) and I was rarely tipped for that so I like to tip for it now.