I have met people who are allergic or say that they are to almost any food that one can name. Add foods barred because of religious reasons, and personal dislikes- "I won't eat fish bait" (suchi).
The only way to be 100% safe with guests is for them to bring their own grub.
Off hand-
Wheat flours
Celery
Cucumbers
Black pepper
Oranges
Sulfites (someone mentioned bacon, above- most cured meats from your grocery or deli have it)
Cheese
Eggs
Vinegars
Milk
Red wine
Yogurt
Peanuts
Corn
Sulfites (in most commercial cured meats)
Dyes in foods
and lots of other stuff as mentioned by Carol C.
Canola cooking oil

(mine? vinegar)
Once had a fellow employee who became seriously asthmatic if someone peeled an orange in the next room. And a boss who was affected the same way by cucumbers.

Succotash- haven't had it for a long time- I bought a fine, big yellow flesh squash yesterday, and I think I will make some.
Firm, yellow Squash is so easy- Cut in half, microwave until just soft, mix with butter and salt for a veg.- or mix with butter and demerara sugar for a dessert. And good hot or cold.