A backup body is nice just in case, but I'll bet you find the RX100 almost as good and easier to carry as a backup in most cases.
While I have a t1i as backup, it only comes with me if I'm taking all my gear (driving vacation etc..) or if I'm going to be taking family portraits or similar. Otherwise for general shooting/snaps the S95 is easier to carry and just fine. I have used the t1i twice this last year when the 5D got an err80 problem and was glad I had it. The question in my mind is how often would you take the 7D with you as a backup? If you're not likely to, I'd call the RX100 your backup and for a 5% general walk around, I'd take the less bulky Sony anyway.