There were no British Half-Sovereign coins minted from 1938 to 1979 inclusive
Without knowing what the particular stamp is and it's condition, it is impossible to value. There was more than one stamp issued during WW2.
The value of a 1943 not canceled 3-cent stamp can vary depending on its condition, rarity, and demand among collectors. Generally, a mint condition example could be worth anywhere from a few dollars to over $10. However, if it is in pristine condition or has unique characteristics, it could fetch a higher price. For an accurate valuation, it's best to consult a stamp catalog or a professional appraiser.
The tulip stamp was marked as the F Flower stamp. It has a face value of 29 cents.
The rioting an boycotting were harming British trade.
It is a forever stamp. It is good for the current value of a first class stamp.
Stamp act
The value of a Top Value Stamp, "Toppie," the elephant sign is approximately $42. The better the condition of the stamp, the more money it will be worth.
The British Government passed the Stamp Act to help pay for British troops stationed in the Colonies
Face value of the original stamp was $0.20
50-275 USD or so
Between $100 and $400, depending on the exact model and most importantly, the condition.