3 years is still a fair while in cadets. I'm assuming you're wanting the extra-curric stuff for your personal statement; include debating and mentoring (milk this too and talk about how much you gained out of helping others) then talk about all dem tasty skills you've picked up (even if you haven't) like first-aid, leadership qualities, teamwork, discipline, punctuality etc.
I didn't have too many things I was able to talk about in my PS (football, competitive shooting & army cadets were the only real things I could use) so I just talked about the 'responsibilities' I had (basically shouting a lot), like teaching younger cadets things like skill at arms/first aid, and that sort of stuff.