I went to Los Cristianos last year for a week. I'd been to there before years ago, can't remember anything about the first time there, I was probably 6 years old at the time.
What was done for each of the seven days last year:
1. General walk around and get to know the surroundings, places to eat/drink etc.
2. Hired a car and drove up to Mt. Teide (Not right to the top using the cable car) then back down the other side to Santa Cruz de Tenerife. Got lost there for 30 minutes then luckily ended up back on the motorway and went back down around the motorway to Los Cristianos.
3. Took the hire car again and basically did a lap of the whole island. Drove up the western side first, stopped off in a few places like Los Gigantes and some other places I can't remember the names of, then across to Santa Cruz De Tenerife and back down the east coast to Los Cristianos.
4. Took the hire car again and took two other people we went on the holiday with up Mt. Teide again and this time went up in the cable car to near enough the top. Stunning views from up there, could see Gran Canaria quite clearly on that day.
5. Went to the Jungle Park mentioned in the post before this one.
6. Went on a boat trip to see some dolphins off the coast of Los Gigantes which was pretty good, the bus driver seemed to take forever to drive what must've been a few miles but still.
7. Pretty much spent packing and walking around letting the others do some shopping while being hassled by people who want to sell my a shiney watch even though I quite blatently already have a nice shiney watch and would therefore not need another.
Plenty of bars and restaurants around for you to try out in the evening, whether you want to try local food or eat something you would back home there's restaurants there for almost everything. I spent most of the evenings in English and Irish bars but that's because I'm pretty boring
There's also a Medievil show in a castle in San Miguel or somewhere around there which you can take a bus to. It's only on a Thursday and Saturday evening though so if you want to go to it you'll have to plan when to go to that in advance. More suited to families though, but you do get food and drink while you watch the show.
If you can sit on a beach all day basically throwing away the money you spent getting there in the first place, which I can't, then you can fill your time nicely.