Pitying fools as hard as I can...
1) after auctioning cards, if there is a lower tech card than the card with a food token, which one should I get rid of?
From page 5 of the rules:
"If players draw a lower card than the one that received the free field crop at the start of the phase, remove the field crop without replacement and place it back to the general storage."
You only remove a card if there is a crop on it, so in this case, no card is removed.
2) do we still put a food token on the lowest tech card after the shuffle card turns up?
Nothing says that you don't, so yes.