I'm specifically thinking military materiel and its significance in the outcome of the Allied victory.
Lots of supplies were from the US lend-lease, but the most visible was tanks, lots of them. Of the over 1000 tanks available to the British for the battle, half were from the US.
This gave the British not only a 2:1 quantitative advantage, but also a qualitative one.
This is the only time the M3 Grant shined. Rushed into service as a stopgap, it's generally considered a very flawed tank. It has a very high silhouette. It's riveted armor means those rivets will fly everywhere inside the tank when it takes a hit. It's then enormous 75mm gun was powerful, but the bulk of the tank had to be exposed to use it. The 37mm "anti-tank" gun was underpowered. But in North Africa in 1942 its heavy armor and heavy firepower outclassed most of what the Italians and Germans had to offer.
The M4 Sherman did even better. With that same 75mm gun now in the turret and thicker cast and wielded armor on the same reliable M3 drive train, it had all the strengths of the M3 without the flaws. It was superior to even Germany's Panzer III and IV at the time. (The Panzer III did anti-tank work with a 50mm gun, the Panzer IV was for infantry with a howitzer. These roles would later be reversed.)
According to this concerning lend-lease Sherman Tanks in North Africa,
The first Shermans to see battle were M4A1s with the British Eighth Army at the Second Battle of El Alamein in October 1942. The tanks had been supplied in a hurry from the US which had removed them from their own units. They were then modified to British requirements and for desert conditions. Over 250, in 12 regiments, started the battle.
Probably as important would be supplies of ammo and gasoline, but I can't find much info there. The sinking of several supply ships bound for the Axis forces definitely left the Allied forces with superiority in numbers and supplies by the beginning of the battle.
Another possibility. There was a South Atlantic Air Ferry route/Central African Air Ferry route that sent lend-lease aircraft, to, among other places, North Africa (it supplied lend-lease aircraft to the RAF in the Western Desert Campaign, so I'm guessing that some of these were used in the second battle of El-Alamein.)
In general, the South Atlantic route is interesting... many aircraft were sent either from Brazil or even assembled in Africa (Takoradi, in West Africa) and then flown across Africa to supply planes for North Africa and India.
The Lend Lease was present in the multiple aspects of the North African victories, with the contribution to equip the RAF and in a lesser extent the Royal Navy.
For El Alamein specifically, the tanks have been already developed in other questions, especially the role of the Grant. I will just highlight the role of the Stuart, former in the war, that was a fast cavalry tank useful for recon in the desert and for guarding the colulns of infantry and artillery when they moved.
In artillery, the British army was largely based on national equipment, but the Lend Lease helped in mobility by providing trucks. The same should be accounted for infantry and logistics.