Well if you are going surfing I'm assuming you are goin to Gower so I would say that if the weather is good enjoy the beach, go for a walk along 3 cliffs its unbelievable, make sure you go to Joe's Ice-cream Parlour and have an ice-cream there is one in Mumbles and also on St Helens Road, you will love it seriously!
Have lunch at Verdi's! They have really nice food and an amazing location! You can go for a stroll along the pier afterwards, play at the amusement arcade and there is also an ice-rink at the pier as well.
You can go to the city centre, go shopping at the Quadrant Centre and on Oxford Street there are loads of cafe's, coffee shops and restaurants I would recommend the Kardomah or Eleos Brasserie and Coffee Shop in the Kingsway. There are also McDonalds, Subway, Burger King etc if you for that sort of thing,
There is a Bowling Alley in town also, as well as a Cinema and Plantasia is also a great place to go if you have kids or like monkeys! Both Plantasia and Bowling are in Parc Tawe which is a 5minute walk from the Quadrant Centre.
Nights in Swansea are great and since you are here on a Saturday night you should check out Wind Street, I love Idols (VIP in Idols is fun), The So Bar, Revolution. You would probably enjoy Time and Envy and Flares on the Kingsway too.
You should seriously consider going to the Morgans Hotel while you are here also, it does an amazing sunday lunch for £15 a head, countless celebrities go there and considering its a 5* hotel the food and the surroundings are gorgeous.......I love the toilets there too ,so posh!
Hope you enjoy Swansea!! :)