from one volunteer to another:
1) If you want to take a laptop you can use it in the air-conditioned comfort of Timbooktoo, a book shop, about 10 to 15 mins walk away.
2) A bottle opener would be handy because soft drinks can be bought for D10
3) A small travel kettle would also be useful if you want a brew up in your room.
4) There are inter-net cafes, if you don’t want to take a laptop.
5) There are supermarkets on the main roads. They look like forbidding office blocks even though there is a sign "Kairaba (or similar) Shopping Centre". They are air conditioned so the doors are tightly closed.
6) A market area where "everything is available" is at Serrekunda. It consists of a series of small shops and stalls rather like a bazaar.
7) The water pressure is normally very low. After work I went for a swim so I was wet for a shower.
8) If you have an Orange pay as you go phone a local SIM card may not be required.
9) My prices are converted at D40 to £1. I got D42 from the local cash machines including all the bank charges. Adama Bah got D47 to £1 when he settled up my expenses at the end of my visit.
12) I did not find any post cards at less than D25. 
13) If you use an electric razor a razor plug adaptor is recommended as the socket in the light over the wash basin did not fit my razor plug. The British three pin power point is the standard in The Gambia.