Here in Boston it is common and normal to take your luggage on the buses and trains. A few rules, though, which I think should apply no matter what city you’re in:
Don’t take up any extra seats with your luggage. If you’re lucky enough to get a seat, keep your bags on your lap and on the floor in front of you. You may be a “paying customer” but your suitcase is not.
Avoid rush hour if you can. That’s M-F 7:30am-9:30am and 4:00pm-7:00pm
Don’t block the doors, don’t block seats, don’t block the left side of the escalator (stand right, walk left, keep your luggage out of the “left lane”).
Don’t run over or into anyone with your rolling suitcase. Be aware of where other people are, where they are walking and if they’re trying to get past you.
If you’re wearing a backpack and have to stand on the bus or train, take off your backpack so people can get by you and so that you’re not smacking people with it.
Be very aware of your surroundings. Move your bag when someone needs to get by; be ready and willing to shift if someone needs to get by you; if you’re walking slowly or need to stop to get your bearings, STEP OUT OF THE FLOW OF TRAFFIC.
If the driver or conductor tells you to do something, do it immediately.
ETA: #8 - don’t bring more than you can carry quickly and easily. If you can’t handle your bags by yourself, with minimal slowness, and without making more than one trip on/off the train/bus, take a cab.
Nobody seems to much care in Portland. The Max goes to the airport, so anybody connecting to it by bus would need to have their bag with them. We took our carry-ons on the bus all the way to the Amtrak terminal and no hassle.
I’m a college student in Boston, and I see people bringing luggage onto public transportation all the time. Logan airport is a stop on the Blue Line subway, and South Station (buses + Amtrak) is a stop on the Red Line, so it is not at all unusual to see people on those lines with suitcases and stuff.
If you do decide to take the Washington/Wells station, be sure to check to see if the station is closed for repair work on the weekends. It has been closed several times this year, including today!!!
I just got back from Portland and enjoyed the Max system greatly. The red line to the airport is quite convenient, and dirt cheap. And I don’t think I’ve ever seen a combination light rail/streetcar before.