Personally, I would not add the MAS-36, if like one poster very intelligently commented, you pick one year of the conflict like 1942. The '03 was pretty much regulated to the special situations by then, so I would not use that either. Here is my choice:
K98k Mauser....definitely, Germany, most of the Baltic Axis partners.
M1 Garand or Carbine...remember more carbine's were used than Garand's, look it up!
Type 99 7.7 Japan transitioned between 1939 and 1941 from the Type 38 6.5
No 1 Mark III*...Canada, Australia, and Britian along with the entire commonwealth.
91/30....1/2 the Russian troops that were issued rifles
M 44... too soon in the conflict, not yet issued until 1944!
M 38...principle issued rifle to non combatants for the Russians (i.e. medical, support troops, nco's, etc.), yet made it to almost 10% of the troops. The remaining picked up anything that they found in battle, friend or foe. Less than .5% had the SVT by this time. There were more with pick axes and shovels than SVT's.
6.5 Carcano...Italy was pretty much out of it by now, but????
M95 Carbine...still used at this time by Croatians, Serbs, and some of the rest of the Hungarian federation, even used by some of the Austrian troops. Germany actually still loaded ammo for this rifle right up until the end.
That's my suggestion, and I am working on my own collection:
left to right: first one doesn't count, K98k, T99, 91/30PU, 91/30, M44, M38.
and I've add these in the last couple of weeks:
Already have a M1 Carbine...got put it in the WWII garage with the rest!