The easiest solution is probably to set the profile (in config) so it's asking for min/max 1 item,
Then set the three items to probability 1. (That's pistol ammo, facemask, and the food...set multiple foods to 1 if you want),
Then balance the categories.
Ammo probability 10
Food probability 5
Attire probability 1
Adjust that balance to your tastes but that would mean each crate gets one item,
and that item is very likely to be ammo, less likely to be food, and unlikely to be a facemask.
Just thinking back to your original query, if you have Ammo probability 10 and Attire probability 1 and always get the facemask,
then your profile is asking for more than one item (in config...), and 'AllowDuplicates' is false.
Either tell it you want 1 item, or tell it to allow duplicates.
* Note - Allowing duplicates will result in larger stacks of stackables.
Getting 10 ammo twice will show in your inventory as 20 ammo.