Being mostly Moslem, the Gambians often use the general formal greeting of 'Salam Ali Kum'. The reply is 'Mali Kum Salam'. If you want an elaborate 'cheers!', try this one:

Kin Ding - Kon Dong - Eye deeya - Eye Lamma Lamma

Which roughly means 'Its nice to be nice' (the first bits are the sound of clinking glasses or bottles). Here are a few other key phrases:

English	Mandinka	Wollof	Fulla	Jola
Good Morning	E samma
Good Afternoon	E Tinyan
Good Evening	E Wulara
Hello, How are you?	A bin yadi?	Nanga def?	Ta na la?	Cassumei
Hello, I'm well	A bi jan	Jamma rek	Jam tum	Cassumei Kep
How's it going?	Co tenante?
Well thanks	Te nante
How's today?	Somon dabi di?
Its Peaceful	Kaira bi
Thank you..	Abarake..	Jerre jeff
..very much	..Barke
See you later	Fo nyato			Bakka jm
See you tomorrow	Fo samma
Greetings!!	A samma daaay!
Softly Softly Catchy Monkey	Domanding Domanding Ne Ka Sula Deng Moota	Ndanka Ndanka Moy Jeppa Domi Gollo	Seyda Seyda Nanga Ta Bit'oh Wah Ndoo

Download the Mandinka and Wollof dictionaries and grammar guides here.