"If an angel out of heaven/Brings you other things to drink/Thank him for his kind intentions/Go and pour them down the sink." This line from G. K. Chesterton's humorous (and, unfortunately, somewhat racist) poem The Song of Right and Wrong. While this advice was supposed to be taken about beverages other than those recommended by the poet (wine and water), it also applies to edible items that some Helpful Harry (or Harriet) has very kindly given you, blissfully ignorant that you would never buy this particular piece of fat, sugar, salt and preservative laden muck in a million years.
You could, of course, follow the poet's advice and pour the unwanted whatever-it-is down the sink. Or else you could find some other use for the wretched stuff. This especially applies to things that are too big to fit down the sink. You don't have to eat it. And if you've found some other use for it other than eating it, you can still thank the kind donor and tell them that the item was very useful and much appreciated, without lying.
Food colouring: Small drops of food colouring can be used to tint homemade face creams, shampoos, bath salts and soaps.
Mayonnaise or (even worse) salad cream: We're talking here about the additive-laden sort of mayonnaise, not some top-quality all-natural product. If you get the latter, eat it. The former type can be used as a hair conditioner or as a face cleanser. Rinse it out (or off) thoroughly afterwards to get rid of any smell. A more garlicky mayonnaise/salad cream should be followed by a scented hair rinse to get rid of the smell.
Soya or some other oil of dubious origin, probably bleached and possibly genetically modified: These make a lovely bath oil or a cleansing cream for your face. Mixed with a little vinegar, they can also be used instead of linseed/olive oil as a polish for wood or leather.
White sugar: Personally, I would save this for making jam. However, grainy white sugar makes a good facial scrub - the natural acids in the sugar (what's left of them in white sugar, anyway) exfoliate your skin chemically, while the grains exfoliate by physical scrubbing. An old gardener's tip is to dip a bar of soap in a dish of sugar and use this to scrub dirty hands after coming in from working in the garden. You can also melt sugar to a syrup with an equal amount of water and use this to remove hair from your legs (and other body parts, but you may not want to do a DIY sugar Brazilian "wax"). Wait until the sugar syrup has cooled to body heat (ripping out hair is painful enough without burning yourself), apply it to your legs (or wherever) and pop a strip of cotton cloth (e.g. an old sheet) over the syrupy mix. Leave it to dry, then yank it off hard against the direction of growth. Once you have finished screaming (I won't pretend it doesn't hurt), rinse the residue off with cold water. Shampoo: This is far too harsh for your hair. If you don't have sensitive skin, use it as bubble bath instead. If you do have sensitive skin, add the shampoo to a bucket of hot water and use it to wash the floor and/or the exterior of your car.