kimmypatti, While on the flight you will make out a customs declaration form which will be given to you. It is pretty self explanatory. When you get off the plane you will proceed inside the airport building and get in line to clear immigrations first. That usually only takes a few minutes. Then you pick up your checked baggage and proceed to the customs line.
It is very simple to clear customs. Do not bring in any alcohol. You can buy alcohol in a duty free shop in limited quantities and varieties just before you clear customs. (I've never used it but they say it is there) On the Island you can get most anything you want although you will have to pay. Tell us what specifically you are looking for and we will let you know if it is available on the Island.
Snacks, well most of us probably bring some but it is possible that they might take them away from you. You have never been out of the country so I'll say this. Relax as long as you do not have drugs or weapons the whole process will be very easy. If you go in the declare line they usually go through all your bags. This line is for people who are importing household items and such. If you have nothing to declare which includes most tourists then sometimes they will want to take a look, it is spotty.
Have a good stay. I would say that San Pedro is a great place to have a honeymoon. Good luck.
Somewhere on a beach in Belize