Having a 72 hour kit packed and ready to use is a great idea! Suggestions for what to put in your 72 hour kit can be found here Another list is here Try not to get discouraged at the length of the list- pull together what you already have and make a plan to add to your kit as you can. There is no need to wait until you can afford the perfect backpack or fancy foods- just start with what you have on hand and build your kit from there!
Tip: One blog I read said that the pop top cans they had stored in their 72 hour kit popped open unexpectedly and they opened their backpacks to a sticky mess. You may want to store traditionally sealed cans and a can opener in your kit instead....