What should I do to put on my university resume later?

Universities don't really care about your résumé (aka. CV), and any single thing like DoE certainly won't in and of itself make or break your chances.

You can include any part-time jobs you may have had, whether paid or volunteer, as well as any sports activities and clubs that you do regularly and over a longer period of time (ie. months or years, not just a few days or weeks). Also include skills such as languages, IT, music/art (eg. if you play an instrument to any of the Grade levels), etc. Nobody expects you to come up with lots at your age, so don't feel bad if it looks a bit slim at this stage.

That depends - what do you want to do at university?

Your university personal statement will generally be improved by doing something relevant to your studies; for example for care or medical professions, care volunteering or experience would be beneficial.