I wanted to write about internal use of H2O2 but of course P&L beat me to it.

Also the advice of buying the 35% foodgrade and then diluting it to 3% is the best idea.
It works fine.
Thanks for posting this thread and of course: See to it that you have enough for when times go bad.
If you buy a litre of 35% foodgrade you can dilute it to almost 3 gallons which will last you for a long time although I would not suggest to dilute it all at once as H2O2 is rather unstable and you may end up with 3 gallons of normal water and a puff of oxygen escaping on opening the botle.
It should come in a dark bottle and be stored in a dark place.