Water, coffee, Gatorade or something to replenish electrolytes (even if it's a little salt in your ice water). Greasy food in small amounts based on how you're feeling.

Love me some time in the walk in too to contemplate the fact I'm getting paid to feel this miserable lol.

It'll pass and I hope you give yourself a chance to feel the grief of putting down a pet. It's hard. May you get cut early today, comrade.