Last month we went on a road trip looking at colleges for my son. At one motel in San Diego they had the worst shower I can remember. It was designed for vertically challenged people and the flow was so low that it took a very long time for each person to take a shower.
A long time ago I used to take a shower head along when I rented ski cabins or condos and I am going to start doing the same when I go to a motel. Just an adjustable wrench and a modified shower head is all that is required.
Not all shower heads lend themselves to modification. Twenty years ago there were shower heads with removable restrictors where the instructions advised you to be sure to replace the restrictor after cleaning the shower head so that the water saving feature would still function (wink, wink). Not sure if there are any of those still around. I bought an inexpensive, solid brass shower head at Home Depot for $18. I removed the water-restriciting rubber washer and replaced it with normal washers . Then I disassembled it and drilled out the water restrictor hole, increasing the diameter by about 4x. I would not try this with a plastic shower head and many of the shower heads sold at Home Depot, even the more expensive ones, are plastic with a metal coating.
Apparently this is all going to get worse. In NY, they already have reduced the GPM for showerheads to 2.0, from the federal guideline of 2.5.
I saw a shower head on Amazon that is supposed to be 4-5 GPM (apparently it ships with a restricting washer in order to stay legal).
I don't get these low-flow shower heads. It just takes far longer to take a shower and you end up using the same amount, or more, water. They need to rate shower heads in gallons per shower, not gallons per minute.