First, put the tame item in the zero slot; the pego steals the zero slot item first.
Second, the amounts given on the calculator are completely incorrect, a pego takes several stacks of mejos, more with levels. Additionally, it has the passive tame bug where advanced crops don't work, so don't even bother with them.
Finally, once tame a pego retains its inventory from during the tame, so if it took anything it didn't eat you can get it back, including any misspent advanced crops.
When you see one, put any kinds of berries in your last inventory slot and walk up to them slowly. They will take the berries and it will add to their bar. Just keep doing that over and over
-bboss505 (pls up-vote
'You have been robbed! 5 fiber'
Ah, look at it run with the little bag
'You have been robbed! 3 wood'
I dont need that anyway
'You have been robbed! 100 narcotics'
O HELL NO
'You have killed! Pegomastax lvl 10'