Mainstay ration bars are not individual wrapped but I think that the Daytrex ones are.

These rations once opened and then re-stored in a air tight contained such as biscuit tin should last 1-2 years.

These ration bars are really just empty calories and lack the nutrients for long term health. They are also expensive to purchase for what they are.

They typically cost around £5-6 excluding shipping in the UK.
They are acceptable with regard to taste but do not compare to something like All Butter Shortbread such as McAlisters
shortbread fingers I can purchase for £0.39 per 150grams or £1.95 for 750grams for 3900 Kcal.

I then just vacuum seal 5 x 150 gram pkts then place in a sealed mylar bag with an oxygen absorber.

Maineprepper wasn't impressed with the Mainstay rations

http://www.youtube.com/watch?v=uJyUyxeoeM4