In general, the stuff model kits come packed with as cargo is more often than not quite ridiculous. This is especially true for Matchbox's LRDG kit: the cargo for the Chevy consists of a bunch of appropriately sized crates, a dozen Jerrycans, sacks and petrol barrels.
Now, both photographic evidence and logical considerations clearly speak against the use of petrol barrels: have you ever tried to load a barrel full of petrol on a truck with pretty high ground clearance without using a forklift? It should also be noted that vehicle fuel throughout the war was issued to British troops in the dreaded 'Flimsy' cans, stowed four in a small wooden crate. While every Allied quartermaster was more than happy when a German supply depot was seized and a couple hundred Jerrycans fell into his hands (the Jerrycan being the only useful design for carrying petrol in those days, and still being used to this day), one should not overdo the use of these cans on British vehicles. (Flimsy cans are available from Raventhorpe in 20mm scale).
Similar considerations forbid the use of sacks on patrol cars: I have never seen a photo of a patrol vehicle loaded with sacks, and it seems not very practical to carry stuff over rough terrain without a good method of fixing its position in the vehicle.
On the other hand, many pictures show the cargo (and the weapons) of LRDG vehicles covered with cloth to protect against sand; such cloth covers can easily be imitated using very thin paper soaked in  thin paste, then draped around the cargo while still wet (I recommend against using real cloth with such small scales; even the finest fabrics just don't "fall" like real cloth would at that size).

Figure Scales

As you might have noticed from the list of models I've used, I am using figures in a wide range of different scales. Take a look around - not everybody is exactly 1,80m in size. Why should they be in a diorama scene? Additionally, I have found figures of the same scale from different makes (and even from different figure sets of the same make) to vary widely in size - I will provide a picture comparing different scales and sizes as soon as my oft-mentioned camera is up to it.

One of the greatest aspects of depicting an LRDG scene in a diorama is that these guys never had anything like a uniform - soldiers were expected to equip themselves with clothing as they saw fit for the climate. As a result, dress and headgear varied widely, giving the modeller the chance to use almost any figure he likes without taking into account the historical accuracy of the uniform. Headgear included berets, ANZAC-style hats, woollen caps, and anything that was available on the local market. Tommy helmets were issued to the Group, but -judging from photos- very rarely worn. I have found Raventhorpe's line of 20mm heads a great resource for replacing 8th Army or Afrika Korps helmeted heads.
  These pictures document the wide variety of dress and headgear worn by LRDG units