I suspect someone was trying to be a good samaritan, intending to take my knapsack to the Lost & Found (I had just set it down while in the deep playa for about 10min, at the teal vibrating dome). In any case, it had contained my Prius keys, and cost me about $1K to replace. The knapsack has other items that would be nice to get back...
It's a black knapsack of synthetic woven material - it has 3 zippered compartments - the small, outermost compartment had my keys, including my Prius fob.
It also contained my headlamp, a wind-up flashlight, and a flashlight with a bike clamp. A collapsible plate, bamboo eating utensils and a water bottle.
There were other items as well, but those the keys were the main things that I wanted back.