It sounds mad, but many days stalking have been ruined, in the excitement of starting the day, by forgetting to take the rifle ammo or the correct calibre of ammo for the rifle.
I always carry my spare ammo in a leather ammo wallet. (like the MTM Ammo Wallets) This means there is no noise of rattling in my pocket and the tips are protected from damage.
You should always take enough ammo to cover an unexpected problem. You may be a crack shot but sometimes things go wrong. The telescope may be loose or you may have fired through long grass or other vegetation. The bullet can go astray and a deer might be wounded and take off. It is important that the animal is humanely despatched as soon as possible and so you may need extra ammo.
A friend told me a story of how many years ago he went stalking red deer. He went out with the stalker and they had several exciting stalks. Each time they crawled forward into position and the stalker took tremendous care setting up the rifle to make it easy for my friend. But each time he was about to take the shot, the stag ran off at a tremendous gallop. Eventually they gave up and returned home empty handed, having had a most exciting but blank day.
Twenty years later my friend returned to the same place and met the now retired stalker. He said he was so pleased to see him again because he wanted to make a confession. He said ’Do you remember yon day on the hill, when we had all those grand stalks but the beasts all saw us and ran away? Well, I have to confess that I had forgotten the ammo, and so each time you were getting ready to pull the trigger I sat up and waved my white handkerchief until the stag saw me and took off!