When booking a trip with Basecamp most activities are usually included in the price. Drinks, tipping, shopping and additional activities are for extra cost.
You can make payments using VISA and MasterCards at Basecamp. It is, however, good to have cash in Kenyan shillings for tipping and some shopping. If so, a couple of thousand Kenyan Shillings (approx. 20 USD) per day is enough, depending on your shopping mood. Be sure to get smaller notes. In Lamu you are best advised to bring cash with you, as most restaurants and shops do not offer VISA services. There is a cash machine in Lamu town for withdrawing cash.