I went the digital bathroom scale route, after years of fuming because my old bathroom scale kept telling me I was 5 lbs. lighter than what the one in the doctor's office told me.
However, you can get on any old bathroom scale, first by yourself and then with the pack, and subtract the difference--close enough.
Weighing the total pack can lead to interesting results, as it did last summer when the total pack weight came out 2 lbs. lighter than my spreadsheet. I unpacked everything and rechecked each item, certain that I'd forgotten something. It turned out that because I used average weights for my food, the total on the spreadsheet was too high--I had taken the lighter meals. At that, I still took too much food!