The food drops for The Netherlands were a joint RAF-USAAF operation named Operation Manna-Chowhound. As depicted, ground crews were indeed invited to participate. Planes flew without any armament due to a cease fire, but in some cases were fired upon by German troops, however none were shot down.
In the scene where Maj. Crosby and Maj. Rosenthal are having a drink near the fireplace in the officer's club, there is a mug on the mantelpiece with Robin Hood's face on it. This is a direct callback to the 1949 Academy Award-winning movie "Twelve O'Clock High" starring Gregory Peck, a fictional account of a USAAF Eighth Air Force bomber group stationed in England during WWII, in which an identical Robin Hood mug, also displayed on a mantelpiece, plays a prominent role.
Robert Rosenthal's final combat mission was depicted quite accurately in the movie, including his rescue by Russian soldiers, which nearly ended in tragedy as shown. What was not shown is that after he was flown to Moscow, he stayed at the US Embassy, and while there had dinner with US Ambassador to the Soviet Union Averell Harriman.
Although it is correct that the town of Valkenburg in the south of the country was liberated in September 1944, the food drop didn't take place there, but near Vliegkamp Valkenburg, which is an (former military) airport close to the city of Leiden.