How to tell if a pack is too heavy is really very simple.

Pick it up. If you can't, or tears, you have too much.
Put it on your back. If feel pain, you have too much.
Take a half mile stroll. Adjust the suspension.
Repeat that last one more time.

Take a five mile hike one afternoon. If you hurt, you have too much. If you hurt bad, you not only have too much, but you have a pack that isn't the right size for you or isn't fitted to you.

Sounds like you are going through some fairly built up areas. You can move pretty light, shelter, clothes, water, FAK and something like 3-4 days of food. Restore food as needed.