If you really want to buy genuine cuban cigars, don't buy them off the cubans who approach you on the beach - you will be smoking banana leaves. Genuine cigars can be purchased from hotel shops and duty free, and they are so reasonably priced compared to outside Cuba, it's just not worth buying the black market ones. Also, if customs check your box of cigars and there is no security mark/hologram sticker, they will be confiscated and destroyed. Might as well buy the real thing from the shop or duty free (don't bother shopping around hotels, they're all about same price and duty free in the airport is a bargain).
Fun Alternatives: Buy your cigars from duty free - you can use up all your cuban currency there, as it can't be used anywhere else or even changed into other currency anywhere bar Cuba so it's not worth taking it home.
When you land at Cayo Coco airport and go to to collect your luggage - you will notice as you come out of the airport, an official looking lady will immediately approach you as you literally step out of the door. She will ask where you are staying, and point you toward the line of men holding luggage trolleys. You will think that you should give your luggage to them for them to push the trolley to your bus, however, even though these 'porters' look part of airport staff they are only doing this service for a chance of a tip from you - they are not paid by the airport.
Unique Suggestions: If you have any Cuban Currency, it is worth letting them take your luggage to give them a peso or two- it is much appreciated. If you havn't got currency, then perhaps take your luggage yourself to your transfer coach, so they are free to assist others who could give them a tip!
Fun Alternatives: As you may not have changed money at the airport, and will change your money when you get to your hotel, ask any friends or relatives if they have or know someone who has been to Cuba and who has some currency left over - take this with you, and you can tip the luggage helpers.
Scuba Diving- NO
If you are booking a holiday to the Cayos for the fantastic diving that can be had, it may not be a good idea to book the Villa Cojimar. Although I saw it advertised as having a scuba diving centre, there isnt one on site (Now closed). There is one in the next hotel up the beach (think Melia) but it does mean carrying your scuba diving up to there (about 15 minute walk). The scuba centre there will allow you to leave your gear there overnight (at your own risk but our friends' stuff was fine), so if you have booked 5 days diving, one after another you would only have to carry some stuff back and fore.