Quantity of ingredients to make 150 veg sandwiches

(Hopefully someone else can give a more specific recommendation, as I know this doesn’t completely answer your question)

The search term to use when looking for this sort of information is ‘quantity cooking’, and there are websites that have tables for how to cook for 25 or 50 people/portions

Of course, how much mayonnaise or other ingredient you use depends on the size of the bread or roll, but 1TB/sandwich for 150 sandwiches seems to be 96oz.

I have no idea exactly what sort of vegetables that you’re planning on using, but you might want to assemble a few sandwiches, weigh the contents, and extrapolate from there. (I say this because so many websites assume meat or cheese sandwiches, so the vegetable amounts are garnishes, not the bulk of the sandwich; assembling a few sandwiches before measuring helps to average out any errors.

Another website recommends 120 sandwiches per 100 people, but it really depends on many issues, as large men are going to eat more than children, and people eat less in hot weather.