This really is an idividual choice issue. Some like traditional style backpacks, others cross body, others messenger style, others slip the extra lens into a purse or a belt lens case. I carry a lot of gear to the parks including tripod, 3-4 lenses, external flash, sometimes an extra camera body w/battery grip, extra batteries, filters, etc. I need a good sized backpack to carry all that. More important is the strap that I use. Since I use a battery grip on all my cameras, I need a very comfortable strap and I use the Black Rapid system. I always have my primary camera out and ready to go so its imperative that the strap be comfortable. Early in my DSLR career I went to WDW with what I thought was a good neck strap. Within two hours, I had excruciating neck pain and a screaming headache. For me a cross body strap was the answer.