Getting better by resting is being productive. Trying to get things done tends to drag out illnesses for a few extra days for me.
Rest, drink lots of fluids, and either catch up on my watch list backlog or rewatch my favorite movies if I expect to fall asleep. Depends on the illness, but almost all of them leave me physically drained so laying down is pretty much unavoidable.
Food will depend on how the old tummy is doing. If food doesn't go right through me or come back up I just eat normally. I love spicy food when congested to clear out the sinuses a little bit.