We are heading overseas next Sunday, and while this particular cruise is not with RCL it is with one of the cruiselines owned by them. We have cruised the Med before.
All excursions are on the expensive side. You are better to try to find someone to share with although you are probably to late to do that now.
You can use public transportation in a number of areas but be careful and be sure you are back to the ship in plenty of time. They won't wait for you.
As a rule, there is no food allowed on or off the ship. If there are severe allergies involved you may find some co-operation but you will need to contact them prior - otherwise you are not allowed.
No liquor is allowed to be brought onboard either for consumption onboard.
There are any number of people who will attempt to smuggle all sorts of contraband onboard. If caught could be costly.
At the same time, I do usually have candy with me as it's almost impossible to get onboard. (At least the kind I like.)