Is there anything I can eat or vitamins I can take to help prevent cramp??

Ruling out dehydration or muscle injuries, there are minerals that you could be lacking in when it comes to cramp. Firstly, I would be checking out your intake of magnesium, calcium and potassium.

When you're training hard, minerals are often lost in sweat, they enable your muscles to contract and relax - which your muscles do all day long (especially your heart muscle).

New Zealanders usually consume adequate calcium through dairy products, but we commonly fail to get adequate magnesium.
Your body needs calcium and magnesium in a ratio of 2:1. You could opt for eating a mountain of almonds, or spinach but I personally think taking a magnesium supplement is essential for anyone that is training for a sport. Potassium, more commonly found in your electrolyte mixes, and in fresh vegetables and fruits can be obtained through a good diet.

Banana's of course being the cyclists optimal food, aim to have one daily, increase your fresh vegetable intake, use more potatoes and drink water until your urine is clear in the afternoon.