@Redland77 I don't think it is common to backpack using just sandals but you can definitely hike in sandals that are made for it.  I always take some as "camp shoes" backpacking that I can use for water crossings, short hikes and as an alternate set of shoes I can wear if I was to get an injury that prevented me wearing wearing my main foot wear.

The type of sandals that I would recommend are Teva Originals, Teva Terra Fi , Xeros or Bedrock Cairns.  These are all fairly light weight but are pretty good to hike in.   Personally I'm not a fan of the toe strap on the Cairns since it means you need special socks and I'm only pointing them out because other people really like them.