magid

I already have salt, cinnamon, and black pepper for Pesach.
A new flexible cutting board would be in order. Other items to consider include: a big soup pot, an apple corer (if I want to make baked apples), and (if I'm making charoset) something to shred apples with (minced apples are not ideal for charoset).
Walnuts can be bitter; if I'm making charoset, consider using half walnuts, half pecans.
I kashered the microwave this year and never used it.
A 5-pack of machine matza is *plenty*.
One kind of jam would be enough.
Mayo can be useful, though certainly not necessary.
There are plastic plates, bowls, and silverware packed away. Any silverware not in the original bags must be considered fleishig. If I want to get some sturdy disposable stuff for milchigs next year, don't use blue, green, or purple.
Potato starch and matza meal seem to be superfluous to my cooking (or at least, this year I used neither, and I've always had matza meal left over before, while this is the first year buying potato starch at all).
A pareve spatula would be a good thing; get either white or dark green.
If hosting a seder again, get small plain clear glass bowls for the seder plate. Also, consider a matza cover.
People eat less than my capacity to cook for them; there will be plenty of food; don't panic.
Some haggadot are laid out better for beginners; think about that before starting the seder.
I don't care for parsley, so there's no reason to use it for karpas (as long as I don't forget about karpas entirely :-).
Eggplant spreads are a good thing, while whitefish salad is a bit dry on matza.
Butter and cream cheese are not necessary.
OTOH, good olive oil is.
It's nice to have a cabinet for Pesach, but I tend to forget about whatever food I put away there.
It is worth finding hand cream and lip balm that are kosher l'Pesach.
It is also worth getting water bottles for Pesach; I think I was chronically under-hydrated this week.
The Elite brand bittersweet chocolate is far better than the other brand.