Hey there, thanks!
You'll see lots of posts in the forum here at BDW about hidden costs, but don't worry so much in Cuba and especially at the OVEP. There are some extras but nothing came as a SURPRIZE per say.
Depending on the wedding package you choose, you may have to pay for the Notary Public/translation services/legal paperwork etc and for extra people over the amount included in the packages. If you pick the free package you will find your self with a few other extra charges i.e. microphone and sound system. We picked the Pure Elegance package and it included almost everything. Did you receive a copy of the wedding package options and price lists for extras? PM me if you don't have these and I can send them to you. These are a MUST have to know exactly what you will be paying for your big day.
Also, know that there is a day pass fee for anyone coming from off-resort to your wedding (staying at another resort). This means if you are over your package's maximum number of guests, there will be a change for the day pass AND the extra person fee. We didn't run into this issue (everyone was staying at the resort and we only had 28 people and the package covered up to 30) but it seems like a common issue, one that people seem to be surprised with.
I brought a lot of my own decorations... they only have table cloths, chair covers and sashes, and other very basics - you can purchase extra flowers if you like or pick some from the gardens (that's what we did). I brought centerpieces, a cake topper, table decorations, and guest favors (in our wedding colours) which were plenty to decorate the tables. The wedding coordinator met with me in the morning of the wedding and I gave her everything and explained where I wanted it/how I wanted it placed and she took care of everything. It looked exactly as I wanted it, they did a great job!
They do not sell any sort of favors or have any other decoration rentals.. if you want something there - its best to bring it with you. That being said, if you wanted to travel a bit lighter they do have little souvenir kiosks at the resort and you can get lots of little things for 1-2 CUC each They had key chains, pens, small toys etc.
Hope this helps, if you have any other questions please let me know.