In the bar scene in Alexandria, John Mills was drinking real beer because ginger ale and other substitutes didn't look real enough on film. In the final cut (the 14th take) he actually was quite drunk.
The beer that the crew drink at journey's end in the novel is American Rhinegold. Although it's not actually a German beer, it certainly sounds like one. As the war was still a very fresh memory in many people's heads at the time, the decision was made to go with Danish Carlsberg beer instead. In reality, as Denmark was occupied by the Germans in WW2, they would not have been able to get Carlsberg in Alexandria. More likely they would have had the local beer.
When they were pushing the ambulance up the hill from behind, Sylvia Syms fell in the sand (as scripted), but John Mills picked her up and threw her (too forcefully) at the back of the van and Sylvia banged her head against it.
The song that van der Poel sings is called "Sarie Marais" and is used as a regimental quick march by the UK's Corps of Royal Marines. It first came to the attention of British troops during the Boer War.
The Austin K2 Ambulance used was actually four wheel drive and had presumably been converted for the movie using a front axle and wheels from a Canadian Military Pattern truck along with a transfer box and prop shafts. The hubs are slightly different to that on a normal K2 and the differential housing of the live axle can be seen on some shots. It was probably changed so it could extricate itself more easily in the shots where it was bogged down. There's seems to have been 2 Austin K2s used for "Katy" as in some shots it has the driven front axle and in others the original beam axle fitted to these vehicles.
The final scenes have been used in two British advertising campaigns in the 80s. One was for Holsten Pils, interspersing comedian Griff Rhys Jones into the original footage, a la Dead Men Don't Wear Plaid (1982). Carlsberg themselves then later used the footage to promote their lager, colorizing it.
The love scene between Anson and Diana had to be re-shot after the British censor decided that Sylvia Syms had too many buttons undone on her blouse, revealing too much cleavage. Censor John Nicholls had already requested over 80 alterations to the script before shooting and, following protests by director J. Lee Thompson, he was eventually replaced as BBFC chief by John Trevelyan in May 1958. Other additional dialogue cuts included the removal of the phrase 'made a balls of it' and the overdubbing of 'bloody good old bitch'.