In this scenario, the character is, as the only person, aware that in a few days the whole world economy will fall apart. He is likely to lose his home and probably has to flee to another country because of war activities. These war activities will also cause the economy to break down, meaning all currencies and all virtual assets lose their value. However, only a very small percentage of actual production, agriculture, etc. is destroyed during the war, and can be used by their new respective owners.
As I said, the character knows about this a few day in before, and currently has about 5 million dollars. He wants to invest this money in something that should at least keep its value after the big breakdown. However, as he is bound to flee, and doesn't know yet if he will have a car or any other vehicle available, he can't just buy barrels of oil with his money, as this would be rather painful to transport over a longer period of time. So what could he invest his money in?
Edit: Wow, thank you very much for all your answers. I think like I should clear things up just a little bit, as many comments suggest things that would not be possible / advisable in the characters situation. I try to explain a possible scenario which the character could be in:
The world is split in a few (maybe 4-8) major forces. Looking at todays world, I would think of a scenario with the USA & Canada, a south america coalition, the EU, extremists controlling Africa and some european / asian countries, and an asian coalition. At the top of every of this groups are very extremistic people, and there are no alliencas between the different groups, and all of them have about the same strength. Think of it as somewhat similair to the 1984 scenario (only in terms of power and strength of the different groups).
The character could f.e. be european, living in france, and it's very probable that his town will be taken over by another of these groups, and he doesn't really know how the situation will be after the escalation. So he has to flee, maybe even go to more than one of the territories hold by the descibed groups, and find a place to settle down again. Or maybe he will be on the run for several years. He simply does not know in before. So all options like farming or hiding his stuff are not possible. He has to take it all with him, and be able to transport it for a longer period of time, in which he will no always have a car or transportation vehicle available.