Hello Faken, welocme to Stamp Community!

The cancels or postmarks look nice. They are collectible also and addd value.
The others are probably postal stationery (e, not a) and are listed in the Unitrade catalogue in the back along with postcards and envelopes and others interesting items.
Ah, the red 4c King George V (5th) is a #U65 preprinted prepaid envelope or a variant, depending whether it was printed on a #8 sized or #10 sized envelope. Hard to tell now.
The cut squares (cut from postcards or envelopes or postal band wrappers) are interesting to collect in and of themdselves.
See Rod222's thread on SCF here about World Mutilated Stationery.
https://goscf.com/t/19277&SearchTerms=mutilatedfor some ID's on some hard to recognize items.