Larger aircraft carried small first aid kits to offer basic first aid to injured air crew. These kits were issued on a scale depending on the number of crew. The basic design did not change over the war, although it was modified a few times depending on perceived need and the manufacturer. Today we have two examples to look at:

Contents could vary depending on the area of the aircraft they were carried in, but typical contents might include: 3 x iodine ampoules in card tubes; ampoules, tubunic, morphine (squeezed) with original metal case & labels for use with; 4oz tube of Tannafax for burns; tourniquet; 2 x packs of absorbent lint; 2 x packs of absorbent gauze; 2 x triangular bandages; 2 x packs of absorbent cotton wool; 6 x safety pins (boxed) with 2 x camel hair brushes.
The haversack is covered by a top flap that fastens at the front with a single webbing strap and a brass buckle. The haversack’s purpose is printed on the top flap in black ink:

Under the top flap are two further flaps secured with a single press stud to prevent the contents from flying out when it is opened:

The haversacks were equipped with a simple cotton tape shoulder strap:

As well as variants made of woven cotton webbing rather than canvas, these two particular designs differ internally, with the earlier example having a divider across the middle of the interior with loops for the contents:

The later version deleted this in favour of a simple open interior to offer more flexibility in filling the First Aid kit:

The two haversacks are marked under the top flap with manufacturer and date, one is 1941 and the other 1943 in date:

As well as the contents, the packs would have had a card inside with the list of intended items, this example being found online: