Sergeant Hietanen destroying a Soviet tank by crawling next to it and throwing a mine under it - at the eleventh hour when the Finns, deep within enemy lines, were just about to give into panic, lose formation and be almost certainly destroyed. It's considered a CMoA by the other characters as well.
Corporal Rokka saving the Finns by first, out of his own initiative, going to check the vulnerable flank, and then all on his own destroying the 50 man strong Soviet ski company that was trying to flank the Finns. He only has Lampinen to supply him ammo. Bonus points that he's hit in the head by a bullet and momentarily loses consciousness, only to come back around and finish the job.
Both of the above scenes were based on actual events that happened. The destruction of the tank Linna saw with his own eyes. When he was criticized by a reader for writing such adrenaline and endorphin pumping scenes into a supposedly anti-war war novel, he defended himself by saying this is how it was and he's simply retelling what he saw himself.
During the first real battle, the Finns are in vain trying to cut through the fortificated Soviet defense lines. The Finnish charges up the hillside only lead to ever increasing losses. Kariluoto is getting desperate, but Koskela comes up with an alternative plan: while the others give support fire, he crawls up the hill, from hide to hide, and manages to get close to the enemy bunker. There he throws a satchel charge weighting 8 kgs and destroys the bunker, dismaying the Soviets. Kariluoto leads the men into new charge and they manage to take the line and force the Soviets into flight.