Excercises and sports which help surfing skills

I live in an inland country in Europe, far away from the sea. I found surfing very interesting and decided that I would like to try it. I have a full time job so only limited (time) possibilities to go to a surf camp in the summer, but before I go I would like to prepare my skills as much as possible.
I "surfed" this forum and found some relevant topics, but some contradictions as well.
Could you please help me what excercises (sit ups. swimming, etc.) and sports (longboard-skateboarding, snowboarding...) could help to build up a relevant skillset for surfing?
I "surfed" this forum and found some relevant topics, but some contradictions as well.
Could you please help me what excercises (sit ups. swimming, etc.) and sports (longboard-skateboarding, snowboarding...) could help to build up a relevant skillset for surfing?