Some good advice here and on other threads. But...the best advice I can give is to visit the internet desk the first day and ask the person there to help you make sure you have all the right things turned off.
You can avoid cellular charges (and associated data charges) easily by using airplane mode, but if you purchase internet service there are lots of pitfalls where your wifi plan can be used up (auto downloads, syncing, photo backup, etc). The people at the internet desk have always been very knowledgeable and pleased to help you make sure everything is off.