I've never heard of a goose getting sick from eating fresh fruit or vegetables. Foraging geese seem to naturally avoid what's poisonous.
I have several poisonous plants in my yard, and as it's surrounded by Ligustrum (privet, which is poisonous), there's not a whole lot I can do about it. None of my geese have ever shown symptoms of poisoning. One pair even took to chewing off privet twigs, but apparently they didn't eat them, just played with them. They've never touched the rhubarb plants, the conifers or the potato plants.
What's more likely to harm geese is feeding them rotting or moldy fruit and vegetables. Be sure to only feed them fresh greens, and remove the leftovers before they start decomposing. In the summer, cut grass will start decomposing within a few hours.
Also, geese thrive primarily on fresh grass. Anything else is a supplement or a compromise - and may harm them if it's a unilateral diet.
Fatty foods like nuts are not poisonous, but they should not have a whole lot of them. Just like us humans.