A sling will be usefull.
Have you looked at hammocks? Heaps more portable than cots and IMO they look waaay more comfy. Try googling amby hammocks. You can buy them on-line and they'll deliver it to your parent's place. They have a carry case that most airlines treat the same as a porta-cot.

Nappies wise have a look at the MCN forums - they may or may not be your thing but you may as well inform yourself before you commit to buying a stack of sposies.

Really all you need is arms, boobs and clothes - the rest is optional.