You are going to need to buy stuff.
Everything from the food you cook to the napkins, to the ketchup, pickles, peppers.

It doesn’t matter what food you are serving, you are going to need stuff to serve it on and stuff to garnish it with.

Each supplier has their own benefit.
One supplier sells serving dishes in packs of 250 for $22.50.
While another sell only in bulk cases of 3000 for $120.
Supplier 2 might be $100 more, but the trays are better than HALF the price.
But supplier 1 might sell napkins at half the price of supplier 2.
Get to know this stuff.
AND understand that prices change ALL THE TIME.

And yeah, 4 cents for a tray might not seem like much now.
But if you are using 100 to 200 a day, that’s going to add up.
Plus that’s not your only cost to consider.
You really need to get an understanding of cost per units served.

4 cents for a tray, 1/2 cent for a napkin ( figure on 3 or 4 per person ) 1/2 cent for that pretty paper that your stuff sits in the tray, ketchup, mustard, ect. straws, forks, spoons, knives, take away bags or boxes ….
If your costs on the disposable items that you give away for free are 25 cents per unit served, at 100 units per day, at 6 days a week, equals $600 a month.

You don’t don’t want those costs to be sitting at 45 cents per unit if you have a choice.

KNOW your pricing !

At least where I live, it’s usually cheaper ( when they are on for a good price ) to buy drinks at Wally World.  I would say probably 60% of the time.
And again, the difference between 30 cents cost on a drink and 45 cents somewhere else, adds up quick.  So watch your local flyers.