Go to http://www.yosemitesites.com/
It's unofficial, but it will show you when reservations open up and how many sites are available for each day. Camp in the Valley if you can. The Valley campgrounds are crowded, but NOTHING
beats waking up in Yosemite Valley! The official government website for Yosemite Campground reservations is http://www.recreation.gov/
There's also Housekeeping Camp, which provides rustic tent-cabins. Look at the photo gallery to get an idea if it's for you--it means less gear to ship with you:
http://www.yosemitepark.com/accommodati ... gcamp.aspx
You may be able to ship your stuff to General Delivery, Yosemite, California. There's a US Post Office in Yosemite Valley. Call them during office hours for General Delivery mail policy (I don't know if there's a wait limit, but they only keep it so many days I think).
Don't bring food---there's a small supermarket in Yosemite Valley with food. There's a smaller food store in Tuolumne Valley. If you're flying in (Fresno Airport, FAT), you can shop in a regular supermarket before taking off to Yosemite.
gregor wrote: I've read that the Valley campsites fill up within 5-10 minutes, is that true?
Yes it can--for popular days (weekends and holidays) and early Summer. Don't take a chance and figure out when the opening day is ahead of time.