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.

I think #1 is kinda too much. because 行くこと「も」あります。 that も already implies "sometimes" in my opinion because you're saying I normally eat dinner in my house but sometimes I go to a restaurant with my friend. In this situation, も　is like. normally blahblah but also blahblah sometimes. So in my opinion. 晩ご飯はたいてい家で食べますが、友達とレストランに行くこともあります。　or 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くことがあります。 are better.