To start, 5E lists "Rations (1/day)" as dry food, jerky, dry fruit, hard tack and nuts. I'd say that can be considered preserved food. For 5 sp you get 2 lbs of rations that is supposed to last a day. That would be 14 lbs for a week of food which according to my friends is ridiculous even for a simulated fantasy game. Let's start going back editions and see.
In 4th Edition (thank you D&DI subscription) Rations per day are pretty much the same cost, 5 sp but they weight only one lb. If this seems more reasonable that's because it was the standard for a long time.
Long lived 3rd Edition (and it's offspring Pathfinder) have a day of Rations at 5 sp and a weight of 1 lb. There is a notation in these OGL products that rations weigh a quarter of the listed amount when made for Small characters. So Halfling rations weight .25 lb.? This laughable notation was already called out as bunk by my friends. Fine for containers and clothing, but not food. Let's move on.
1st Edition (and perhaps 2E as well) handled rations slightly differently (as well as encumbrance). There was Standard Rations (unpreserved food) and Iron Rations (preserved food). My guess is "iron" was dropped in later editions and was the default ration. Standard rations for one day cost 8.5 sp (4.3 sp in today's exchange rate) and 28.5 coin weight. Coin or g.p. weight was the encumbrance system in early D&D and was an abstract of actual weight and bulkiness. 10 coins = 1 lb. Thus, standard rations weighed almost 3 lbs. That's the unpreserved stuff mind you.
Iron rations which is our focus, come in at 14.3 sp (7.1 sp) per day and weigh 10.7 coins, or a tad over 1 lb. Par for the course right?
And now to be complete, old red box Basic D&D used a similar coin weight system to AD&D. They too had Standard and Iron Rations. Interestingly, the descriptions say standard rations are good for throwing to monsters for a distraction. Never considered that. Anyhow, basic food is expensive. One day of Standard costs 7.1 sp and one day of Iron is a whopping 21.4 sp. Basic rules liked to be expedient with gear weights as they focused on treasure carrying. According to the rules, all an adventurers' miscellaneous gear and provisions (rope, spikes, sacks, wineskin, rations, etc.) weigh 80 coins, a measly 8 lbs! This of course could be chalked up to the fact its not bulky if stored and carried properly. Going by advanced rules, if you only carrieda week of iron rations that would come out to about to 7 lbs. I'm sure rope and bars of metal weigh more than biscuits and dried meat, but hey that's why its basic rules.
Back to the present, why in the world did the 5E designers think rations needed to be upped to 2 lbs per day? I know weights probably fluctuate for all gear through-out D&D's history, but as you can see Rations had been fairly consistent until now. If encumbrance and food is diligently tracked in a campaign, carrying a week of food for these hapless adventurers becomes a very big deal. Is that small bag of gold more important than their next meal? Time to buy a mule.