Honestly it sounds like food, water, guns, and ammo would be the best investment since if the economy were to collapse as you fear it would these would be the items in highest demand, thus their value would skyrocket.
No point in hording paper cash either since it would become worthless if the economy crashed.
Gold wouldn't be a bad choice either, but it would be very hard to trade without broadcasting "I have gold, come rob me!" At least with food, water, guns, and ammo not only do you hold something with tangible value to barter with but you also have the means to defend what you have.