I would go for rope that is a bit thicker, partially because of abrasion concerns but also because in assembling a minimal kit like we are discussing, I want something that is UIAA rated for lead climbing, whatever the diameter might be - currently something around 9mm. You almost are likely to face a situation where climbing up is necessary, as well as rappelling, and you want to be ready for that. I would throw in a couple of slings, and perhaps a small chock or two - it would depend a bit upon the precise situation. As has been pointed out previously, a proper climbing harness is so light these days that it makes sense to include one as well.

I strongly feel that anyone who learns to rappel should also be briefed in at least the rudiments of climbing and belaying, although for someone who cannot climb for whatever reason, an instruction course can be arranged. I have this opinion because I have rescued several "rappelers" who were clearly clueless and in trouble when the slightest problem developed. It's really all about learning how to use rope safely when traveling through technical terrain.

Ideally, anyone going down a rope will have the training and ability to ascend the rope if necessary. This can be done only with prussic slings, along with the appropriate training. More elaborate gear makes ascending much easier, although we are taking about minimal situations here. This is one situation where I might consider paracord, whichis generally best used for and tent lines IMO. I believe there is a case where a rappeler fashioned prussic slings from his shoelaces, and saved the day.