You don't even need filters. Shove ground coffee in a plastic bottle. Fill it with water. Shake it briefly. Leave it in the fridge for 8 hours. Pour the coffee out slowly so the grounds stay at the bottom.
Later on the trip I bought a Turkish coffee maker, which works on the same principle, so it's not so much an innovation as it is a hotel survival tip.
Glad you prevailed! My nightmare scenario is having coffee, but no way to grind it.
And the cupping procedure doesn't even do that, but still produces reliable tasty cups.