Exlax brand had to change one of their products,
a few years ago; I am not sure which one.
They used to have a chocolate bar product,
chocolate itself is a laxative, I think.
Head lettuce keeps reasonably well, if cool.
Raw carrots keep really well; they can be buried,
and they will really clean you out. Cooked carrots
have less laxative effect.

Carrots (and potatoes)
would be a good long term survival-storage food;
keep cool and dark in a make shift root cellar or
just burry them under 4 inches of dirt/sand.
If moles and other varmints are a problem, then
burial may be accompanied with wire mesh.