Rule of thumb on food is 2lb a day based on 3200 cal required for an active male 18 to 35 and 100cal per oz. You may need less calories and you can be more weight effcient than 100cal per oz generally by carrying more oils, fats and things like nuts.

But assuming 2lb a day will give you a weight to test with.

You can get a decent electronic luggage scale on line for about $10.