I always take a back up, even when I am close to home. On stand, with short carries, I will carry both out and keep one tucked to the side just in case. I don't mind waiting until I get a next to perfect shot, even if it means I go home empty that night, but not being able to take the shot because of something wrong with the primary gun would be wrong, but distance and terrain determines which goes where. On away from home trips, I carry 2 ATR 100s. One in .308 and the other in .30-06 (my primary).
If it comes down to walking, short (under 200yds) shots, then I take my Rem 799 in x39mm (lightest rifle I own), backup for that would be my 340 in .30-30 (it is heavier than my 799).
Close country / pushing bush (shots +/- 50yds) heavily-sported 1898 Lee Enfield Carbine backed up by a Jungle carbine.
Longer shots (+/- 400yds) get the nod for the ATR in .30-06 and this year to be backed up with a Ruger M77 chambered the same. Long shots (in excess of 400 yds or so) are no longer in my bag of tricks since I don't want to have to go that far over tough ground and then drag them that much further to the truck, not even deer ... maybe rabbits or coyotes...
Usually carry an SKS and a 10/22 in the truck year-round, so they would be there, too. There are a lot of milsurps in the cabinet that, unfortunately, don't get the nod anymore (unless they are loaned to first-timers) even though I have hunted with them all over the years. All of my children learned to shoot centre-fire on a drastically lightened, but nicely sported, #4. Two of them took their first, and only, deer with it and my son has used it for years (it would have been the wife's moose gun this year, but, alas, not drawn).
I have a couple of P-14s I am working on to make them matching his and her moose/elk rifles. So far, both reamed out to .303 Epps (both were already sported), excess metal (shortened barrel, rear sight and ears, knob on bolt handle drilled out), removed on one, stock cleaned up to fit her hands and LOP shortened. Dayton Traister triggers ordered. In a few years, should have nice rifles. Until then she hunts with a Savage 111 in .243, or one of the #4's.
There was a time when a back-up did not exist for many years, now, not taking a back-up is inconceivable.