Omega Strike

In the hub area of Tumbleweed, there is a butcher in the center of town. Talking to him allows you to buy three different items. For these two achievements, you need to buy a Chicken Treat and a Grand Feast at some point. These are consumables added to your inventory (they aren't immediately consumed), so feel free to buy them whenever you have extra money. Or, wait until you buy the weapon upgrades, since those are more important, and buy these before heading into the final area for the final boss fight.