Back up gun?

In the area I live it is time for ground squirrels. We have a relatively short window to shoot them, usually about 3 months and it is over. The heat drives them back underground.
So last Sunday was pellet day on ground squirrels. I really like going for a walk and stalk for these things. Our ground squirrels are smaller than most. They are 4-5” tall and an obese one is maybe 1 1/2” diameter. So they present a rather small target. I had a ball sneaking around shooting prone and sitting with my Compact 22. I think anyone who shoots primarily slugs like I do should occasionally revisit the fun of a pellet hunt.
Today was slug day. Grabbed the M3 and as I was loading the M3 into the truck I thought grab the compact as a back up gun. In goes the pellet shooter.
I had a rough week and was really looking forward to getting out to a new quiet spot I had scouted up. Well well well! My quiet area was over run with road hunters and walking hunters. Some secret. Oh well went to the spot I had decided on and after waiting for 2 truck loads of bubbas to get past the squirrels started popping up. I had a great shoot and I was shooting very well today. After 4 mags through the M3 I decided i wanted to use the pellets. Wanted being the operative word here. I had forgotten to throw a tin of pellets in. It didn’t ruin the day but man was it disappointing.
Anyone else do this? Maybe not ammo, perhaps your air bottle, cleaning rod or other necessity?
 
I'm so anal that virtually every time I go out to shoot the back of my car gets packed with my 3 rifles, 3 air tanks, ammo boxes (that never leave the car) bipods & airgun tool box. Once I left a bipod at a property after shooting (got it back) but don't think I've ever been "without" or lacking once I got there. It WILL happen one day, I'm sure.