The following are some notes on general issues that should help in sorting out a trip to the island. Being uninhabited means that you need to bring everything (and I mean everything) with you. It also means shipping out all of your waste.
Probably the easiest way is to drive to Oban and get the Cal-Mac ferry to Castlebay. You don’t need to take your car over but this means that you will have to carry everything on board in one trip - big rucksacks and holdalls!! For foot passengers this ferry is just turn up and pay - no booking involved.
Once at Castlebay you will likely have to camp the night there before getting the fishing boat over to Pabbay the following morning. A good time to stock up on food. However note that the Saturday ferry gets in to Castlebay at 20:30 and the shops shut at 18:00 only to open again at 1200 on Sunday so you may have to arrange the boat to Pabbay to take account of that. Things aren’t cheap out here but slightly better than carrying on to the ferry plus you are helping the local economy. The trip to Pabbay is about 45mins.
Note that some of the locals pronounce Pabbay something like Papaya or Papayuh though most say it as it appears to English eyes and ears.
Pabbay is completely uninhabited, no summer shepherds or fishing outposts, ergo no facilities. Either take a folding spade and dig a deep toilet pit a long way away from, and downstream from, the drinking streams or take a small chemical toilet with you and take your waste back out with you. There are facilities in Castlebay for camper vans to empty theirs and you may be able to use those. Generally, look after yourself well (see Health below), wash your hands etc), as picking up a dose of the runs here would be extremely unpleasant!
Your tent should be reasonably strong - no need for a full mountain tent but equally that festival special from last summer may not be up to the job! Remember that you are going to be there for a week so something that isn’t too cramped is preferable.
We felt that the camp site down by the sheep pens would be too midgey so camped closer to the landing point on a spur. As it turned out, about half the usual camp site flooded whilst we were there.
Some form of camping chair is useful for the evenings as is a larger community tent - you only really need the outer.
Cooking and Ordures
Try not to use washing up liquid, Bi-carbonate of soda is a bio-degradable alternative. Again dig a drainage pit some way away from the campsite for washing. Also food waste attracts vermin though we didn’t see signs of any, so in general be as neat, clean and tidy as possible, dig a pit for waste cooking water and the like. Preferably pack out kitchen waste - you had the space to bring the stuff in.
With the island being exposed(!) to the Atlantic winds, midges are not as big a problem as might be imagined but given a still evening... Ticks are said to be prevalent on the island but we only had a few bites plus about the same number caught before they attached. Long trousers and decent shoes are in order and try avoiding lying directly on the grass in the camp area and don’t leave clothes lying on the vegetation. If you are selected as a host then see here on how best to remove them. I am not sure if Lyme’s Disease is a problem - the only possible mammal host that we saw was a solitary sheep.
In addition to the above, it is probably best to treat the water on the island as unsafe, getting sick would be more than a little uncomfortable. Boiling (possibly bring extra fuel for this), chemical treatment such as chlorine tablets or a filter/UV system like the Steripen would be in order. When it rains the runoff is pretty quick and the water in the burn turns a peaty brown but is otherwise OK - we boiled it but didn’t filter it.
Of course each group, and pair of climbers, should have a first aid kit and at least some basic knowledge in how to use it. For emergencies consider hiring a satellite phone.
Odds and Ends
The usual long term camping stuff such as plenty of alcohol and a good book to read are also worth taking, the latter in case of bad weather, the former in case of a good time! If you aren’t a twitcher then one of the many bird field books may be worth taking as well. Also worth ensuring a good supply of batteries and film/memory cards for cameras, this isn’t the place you come to often. If you have a lot of electrical equipment then a solar charger may be useful.
Rope protectors are essential - our abseil rope showed signs of wear with just a couple of abseils over an unprotected edge.