I agree with Danxg. It would depend on one's circumstances and ability. And it will be difficult to quantify how much exactly because under such situation, which we will have no control of, even a truck load might not be enough. But I sure do hope that we will not reach that extreme situation because no one can really be prepared for that.
This guy is ready for a collapse http://www.telegraph.co.uk/earth/greenerliving/7951968/The-man-who-lives-without-money.html
That's pretty funny... he doesn't use money, but he wrote a book that he sells for.... money: What a dweeb. He just refuses to use anything other than labor or like-kind barter to facilitate an exchange... which is pretty irrational. Let's say his neighbor grows tomatoes that he wants. He goes to the neighbor and says, hey, trade you for some tomatoes... is there anything I can do for you for some tomatoes? Neighbor looks at him and looks at his stuff, and says, Nah, I don't really need your help with anything right now, and I don't want any stuff from you, but I'll tell you what: give me 200 acorns and I will give you 5 tomatoes. No-money-man says, OK, I can get acorns, but what you gonna do with them acorns? Tomato-man says, I'm just gonna hold on to 'em, and maybe next week I'll trade the acorns with cow-tender-man for some milk that I will drink. Presumably, no-money-man won't make the trade because the acorns will be used as "money" (store of wealth) rather than as a consumable. He's just an asswipe who is checking out of organized society. Which is fine, and his right. But, then he's trying to sell his story and his book (for cash money).