Using My iPhone 4 Abroad?

Hey guys, I'm going away on holiday to Italy next month and was wondering if anyone could help me with my concerns about taking my phone. I have an iPhone 4 and I'm on a 12 month contract with Tesco Mobile. I get unlimited texts, 250 minutes and 1GB of internet each month (and free wifi). I want to take my phone on holiday to play the games and things on it, but I don't want to end up with a hefty bill at the end of it because I accidentally used internet/services that cost me a fortune. If anyone could help or share past experiences, advice on how to ensure there is no big bill would be much appreciated!<3