20 - 25% of body weight should be a maximum, so if you weigh 10 stone, 140lbs then maximum weight should be no more than 35lbs.
Make sure that most of the weight is carried on the hips and that the bag on your back is "top heavy"
Bugging out is a last ditch thing, leaving your home is not something recommended unless it cannot be avoided. I was evacuated once because of a major fire a few hunderd yards away with toxic fumes, all windows and doors were locked before leaving, even on the third floor!
Normally a bug out should be no more than three days "wlid", after that either get back home or find a good hotel and have your insurance company pick up the tab, providing you have proper insurance that is, have their phone number and your policy number handy.
, I have several these days, I used to have the Army bergans, but went for no DPM (Camo) stuff as it draws attention, plain black or green, or multi coloured panels are better, never get a bag that is too big for what you want to carry, otherwise it all ends up in the bottom giving low centre of gravity or you try to fill it and it gets too heavy to lift and carry.