I usually use a dirty t-shirt, or a bandana. And just keep it in a drawer beside the bed until it gets too stiff.
Now that I am a little older and wiser, I try to remember to bring a bandana with me whenever I go on trips. As I know I will need to nut eventually, and better to have something on hand to nut into, rather than having to run to the bathroom after. Especially if I am traveling with people, camping, or staying at someones house.
My best friend and I used to share a cum rag for a while. Right after we both graduated from HS and we were 18, I stayed over at his house pretty much that whole summer. His dad was a single dad would be at work all day, we would have the run of the house, lounge around in our boxers, and put porn on the TV. We never jerked off together, oddly. I think somehow that would have crossed a line for both of us at the time. But we would get hard, tent up, and rub the tents from the outside of our boxers. Eventually one of us would say 'Ok! I'm gonna go rub one out' and go into his room and use his pillowcase/turned cum rag. We would both use the same one. Sometimes if we were horsing around we would throw it at the other person to get their attention, or if they were being a shit.
Eventually during that summer we decided to see how long we could use the same cum rag. The pillow case eventually lost all playability, and became a sculpture. So we displayed it proudly on his dresser. God we were gross dudes back then