I also think about this when hunting. Mostly as I'm holding on to my .50 cal and watching squirrels run past me during deer season.
In Illinois the laws do limit the firearms we are allowed to carry. .45 is the smallest caliber legal for deer. As a law abiding hunter I do only carry the legal weapons, but there have been lots of times, legality aside, that I would rather have more choice in the matter.
I consider the same thing when squirrel hunting, as I often see deer walk within in range. however .22 is not legal for deer.
I sort of wish they would modify the law a bit, so that some medium caliber gun would work for both. Something in .32 or .36 caliber would work pretty handily for squirrels, and still make a possible shot on deer.
Of course in Illinois you can't hunt both at the same time anyway, so in the end it's all just thoughts I have while sitting in the woods in the wrong season and with wrong gun.