J.,
The absolute best buy I have made amongst all the "baby stuff" has been my Snugli backpack. It's not a hip carrier or sling (I had previously bought a Bjorn carrier and two other sling type carriers which I never used). The backpack is great! I use it for everything from hiking to shopping to traveling. I just traveled to California with plane change by myself with my 9 month old daughter and this backpack. I love it because it has a little kickstand so you can set it down on the ground with the child still sitting in it. It also has a little compartment in the back which can hold some diapers, wipes, a few small toys and food. It has a nice hip belt which also has a little pocket you could put a wallet, keys or a little cell phone in. It also fits nicely into the overhead compartment on the plane. It leaves your hands free and my daughter loves to sit up where she can see everything going on. The backpack is comfortable (or at least as comfortable as it can be when you are lugging extra weight around!) and both my husband and I can use it.
I got mine at Babies R Us for $60-80. There is a Snugli brand that is more expensive, but from reviews I read, not really worth the extra money. If you are interested you can look it up on the Babies R Us website and read some other reviews of it, but like I said, for me it was money very well spent. Oh yeah, I also use it around the house when I am vacuuming and sometimes my daughter falls asleep in it while I'm getting housework done!
P.S. We were living in the San Diego area until about 2yrs ago, but are hoping to be going back soon. Have fun on your trip, I absolutely love it there!
J.