San Francisco

I have decided to go to San Francisco with my friend Kathy and her brother David. Every year David comes to Texas from Paris and they go on a big trip together. I really like David, he is a pretty cool guy and he is about my age. He is also gay and has a b/f of like 5 years. The boyfriend is not going to be coming to TX with him so it should prove to be an interesting time. We don't really have any set plans but we have already agreed we will be going to the gay bars at night. I am not sure if that is going ot happen b/c he normally doesn't go out so I may have to hit the bars on my own. Which won't be a big deal because I usually do that anyway during the trip I take by myself once a year.
I have already told them I would probably be separating myself from them during one or two of the days we are there so they can do the brother-sister bonding and I can do the stuff that I want to do. Knowing Kathy and David we are going to have plans for every single moment of the trip but we are really not going to do anything. I love Kathy to death but she is not the best planner. And even when she does plan her plans usually get changed by the wind. 

I can't wait, I am very excited about this trip.  There are a few things I have to do to prepare for my trip:
1. I need to find a cool messenger bag
2. I need to buy some cool dress down/t-shirt type of clothes. (I will need Ivan's help for this)
3. I need to loose at least 10 lbs. (David is very skinny and I don't want to be the fat friend). 
I think that is all I need to do.

Have you guys been to San Francisco? Do you have any suggestions on what I should definitely see while I am there?