I'm not sure about gas stations, but the MTA vending machines in New York City accept a zip code of 00000 for foreign cards.

You'll be able to use your credit card at gas stations, but you'll probably have to go inside to do so; you won't be able to pay at the pump. Last summer I used my German credit card at pumps in the US, and it invariably failed on pumps that asked for a zip code.

@phoog They didn't when i tried it last December.

I've been able to input a five-digit number (well, actually, my home postal index which accidentally matches the US zip code in length) and it has worked.

Sweden also has 5-digit postal codes, so maybe that's working out in my favour.

I am USAIN living in the USA. The last couple of times I payed for gas, it just worked without a ZIP code. Maybe you don't need to do that anymore.

FYI Tipping valets is standard. And I would say, for hotels, more universal than tipping bellhops (which many hotels don't have) is tipping housekeeping.

Note that it's always possible to take your own bags to your room, eliminating the need for tipping bellhops.

I'm not sure if someone attending a conference would afford a hotel with a bellhop; I certainly never had a hotel where someone carried my bags for me when my employer was paying.

How about buses? I've taken cash-only buses for anything from $1 to over $50, in both small towns and big cities.

@phoog I can confirm the MTA vending machines accepts Swedish zip codes, it worked perfectly fine for me after I realized it asked for my zip code and not my pin

@DJClayworth I think what worked for me in those machines was pressing Enter (i.e. leaving it blank and therefore skipping it).

@gerrit I thought about buses and other forms of public transit, but in the context of the OP's question, he mentions a rental car so I skipped that.

Is tipping in hotels common? I've never done so and never knew it was an issue. I usually stay in hotels 3-4 times a year and never suspected tips were needed.

Tips for housekeeping staff is expected in US hotels, yes.

@bob0the0mighty In the hospitality industry in the US in general, tipping is very common. Bellhops, room service, anyone bringing something to your room, valets, concierges, the guy who whistles to get you a cab, the guy who makes a quick sign to get you a cab... Look at the taxi line at a busy hotel and count the number of "handshakes"...

I have to admit I still have a hard time with the housekeeping staff tips... I do it regularly especially on longer stays, but definitely not all the time.

@jcaron - really I would say the gas station problem is now, 2020, "largely historic".

@Fattie I'm from Germany and just got back from a visit to California last week and both my visa and mastercard created the prompt for ZIP code at 4 different gas stations all over the country and neither blank, 00000 nor my 5-digit zip code, nor the local zip-code did work. I always had to get to the counter and explain to the annoyed clerk that it didn't work.

Never in my life have I seen a bellhop.