If I'm going for a weekend i just bring a brush and use whatever bar of soap there is at the hotel. Not ideal but it's fine for a few days (or i just don't shave that weekend)

If I'm going for longer than that I bring one of (or half of one) these: https://www.amazon.com/Van-Hagen-Del...1920935&sr=8-5

and use it with one of their mugs. I just leave it there when i go.