I'll give you a straightforward answer. If you have no control over the source of the animal products, then my recommendations would be to cut out everything except beef and dairy. In terms of priority, I'd recommend cutting out fish, chicken, and eggs first.

My rationale:

• Looking at total number of animals killed, fish/chicken/eggs dwarf everything else
  • Beef and dairy ranked last when someone attempted to quantify suffering caused by animal foods
  • Beef cattle, generally, have an okay-ish quality of life for 12 months of their lives (typically 12 months on pasture where calves and mothers are kept together, and then 6 months in a feedlot before slaughter)
  • Dairy cows produce huge volumes of milk per cow. The dairy industry is inherently cruel, but it impacts fewer animals overall.
  • For other animals, it's almost a guarantee that quality of life will be extremely poor for any cafeteria food: eggs will have come from battery cages, chickens/pigs will have come from factory farms, etc.

Obviously, it's best to avoid all animal products as much as you possibly can, but if you're choosing between fish/chicken/beef, all of unknown origin, I think the safest bet is that the beef would have probably caused the least suffering. However, none of this can be used as an excuse to knowingly purchase animal products when you have other options.

Another way of looking at it, taking into account accidental death through harvesting feed crops: - Animals killed per 1 million calories