A lightweight variation on this is to pre-mix and pre-soak your own Bircher at home. (We love Carmen's!) We use ruby grapefruit juice as the soaker - gives it a lovely tang. Once soaked overnight, we mix in plain natural yoghurt and some stewed fruit of choice.
Now for the secret, which we've basically adapted from Frank and Sue's great bushwalking food e-book - as advertised on this forum
We dehydrate the mix in our food dryer - on medium overnight - then vacuum seal it and pack it for walking. I can't recall the exact weight saving, but it's considerable.
Once at camp we rehydrate it with a bit of water, and usually cook it like porridge, sometimes with added dried fruit and/or nuts. It's very tangy and nutritious. You can have it cold of course, as long as you have re-hydrated it well. The hot version isn't a purist's Bircher, but by golly it's delicious
and it keeps you going for hours.
cheers
Peter