They're just showing samples. #34 is an ammo sling/bandolier with five pockets that held two five-round stripper clips each (the SMLE has a 10 round magazine). So that's 50 per bandolier. Two bandoliers were worn for an assault - plus the 10 in the rifle is 110 rounds. And if they were planning on holding they might carry additional bandoliers.
Remember - there was a lot of stationary work for the rifleman in WWI. The heavy machine guns did all the shooting.
Nice Find ! Personally I Would cut the Entire Top Lid off at the seam.
That way I Could See what's all in it, Besides Dirt, &
Place the lid back in place when Desired.
my guess , like most containers, Dirt Has seeped in & Packed Tight around Everything
I used Evaporust on some old firearm barrels and it worked great. I might be tempted to immerse the entire box in Evaporust for a few hours. No steel wool or wire brushing needed. You need to do something before it rusts away.