Warning Do not eat any wild food unless you can positively identify it.
Sumac is one of the easier wild foods to identify though. It has red clusters of berries rising above the foliage. Don't worry too much about poison sumac, for while it shares a name, it has white berries, not red ones.
You will want to collect the clusters during a dry period, as rain can wash out the acid that makes them sour.
Collect as many as you think you will need, but keep in mind that 1 cup of berries is only about 1 1/2 teaspoons of spice. It shouldn't take very long to collect all the berries you need for a years cooking.
Let your berries dry in a cool dark place for a week or two, as this makes the spice much easier to seperate from the seeds.
You will need,
1- sumac clusters
2- a sifter, strainer, or colander
3- a blender, herb grinder, or food processor