If you MUST fly, that is, you NEED to fly, then these are minimal precautions. I'd want to wear an aspirator (I have my own), hopefully they'd allow that too. I'd also bring on my own food and water. It's worth going an extra couple of steps if it reduces contacts with others.

I've seen the 'mid air refuelling' option discussed elsewhere, and apparently its way too expensive. Not to mention the potential safety issues should something go awry - two planes at 20,000 feet 10 metres apart with hundreds of souls on board, what could possibly go wrong :-) ?