まずはじめに、「行きこと」ではなく「行くこと」が正しいです。
This も basically means "too / also".
2.晩ご飯はたいてい家で食べますが、時々友達とレストランに行きことがあります。
It says that "I normally have dinner at home but sometimes there are cases I go to the restaurant with my friend(s).
1.晩ご飯はたいてい家で食べますが、時々友達とレストランに行きこともあります。
It says almost as same as 2., "I normally have dinner at home but sometimes there are also cases I go to the restaurant with my friend(s)"
However, it can give us the nuance that there maight be other options but not always.
I hope this helps you to understand its difference.