I think some of it depends on your minhagim. Do you use any processed/canned goods? Do you eat milchig? Etc. Also, the number of people and ages will impact what you need.
You'll likely need disposable plastic containers: 3 oz, 8 oz, 1 lb, 2 lb. Convenient for *everything*.
More disposables: foil pans of all sizes, foil, plastic wrap, vinyl tablecloth, 5 oz. cups (for sedarim), larger cups, bowls, plates, knives, spoons, forks, Ziploc bags in quart and gallon sizes, plastic baggies, twist ties, paper towels, stove foil, soup bags, counter covers, etc.
Like someone said, every year you can buy some non-disposables to replace the disposables. This is our 20th year making Pesach, and we still add to our kitchen equipment one or two things each year.
At the very minimum, start out with a good chef's knife and cutting board. The knife, almost singlehandedly, makes Pesach food prep less burdensome. Peeler, paring knife, two fleishig pots, frying pan, utensil to use with frying pan. That's the bare minimum.