I used to always take plug-in nightlights for the bathroom. It was enough light to see my way around in the dark. Unfortunately, I'd forget to remove them when I was packing up, so I stopped doing that. Instead, I buy a pack of glow-in-the-dark sticks from the dollar store. It does the same job and I don't need to fret over having left a more expensive item at the hotel.
I also take inexpensive flip-flops to wear in the room, down to the pool, etc. They're lightweight and don't take much room in the suitcase.