Here's some tips:-
(a) It can be cold in Cuba in winter (December) especially at night. Pack some warm clothing especially for sleeping in as some accomodation does not have any heating if you get a cold snap (as we did).
(b) If you are vegetarian then the diet really can be very restricted (though the rice and beans is great).
(c) Cuba has a ration book system to try and distribute basic goods fairly to all. On Jan 4th, 2011 soap, toothpaste and detergent were taken off the ration book so everyone has to pay for these now so popular gifts!
(d) If you climb El Yunque you need to cross a stony river so water shoes or flip flops (if they'd stay on) are useful. Also useful on some beaches.
(e) If you have your own snorkelling gear take it with you. Its supplied on the optional island trip to see the iquana and tree rats (well worth doing) but there are other opportunities to use snorkels where nohire is available.
(f) Hand gel and loo paper ....there are drainage problems in places and some of the old sewage systems are really struggling to cope.
We used our free day in Baracoa to climb El Yunque, 7kms west and 1886ft, with a guide arranged through our tour leader. You walk among coconut trees and cocoa plantations, banana, guava and mango trees and learn much about the local ecology etc. while climbing. About a third of the way from the top a local farmer has a stall with fresh coconut, bananas, oranges for 1 CUC to eat as you wish. It is quite steep in places and can be very slippy though there are some rails at key points. You need decent walking boots. There are no exposed points. A taxi brings the guide to the hotel then takes you to the start of the climb. Nice views from the top.
In Trinidad we went on the optional trip to a Cayo . Idyllic spot with really tame iquanas and tree rats that milled around eating luch leftovers. Fascinating. Snorkelling done off the boat. Guy on this trip mentioned that local horse riding trips to see the valley around Trinidad were available and good.
In Havana there are shows on in the evening at the Hotel Nacional: French Caberet , Jazz, Folk. The hotel has a fascinating history and is really worth visiting. Has a garden bar near the promenade with a lovely view round the bay to Old Havana.