You can often narrow it down by taking what you have eated, how long, and what type of poisoning would typically be associated with the product as well.

E.g. cold meats, deli cheese etc - Listeria, more than 3 days, flu like symptoms, stomach cramps etc.

Potato chips - salmonella (yes, rare, but happens!), 6-72 hours (can also be instant to a month later, but 6-72 hours is typical), vomiting etc.

Diet Coke - Leptospirosis (not from the coke, but from the bottle / can that was stored in a rat infested warehouse etc. again rare!) - jaundice, fever, etc. 2-30 days.

Pretty much any food can be contaminated either when it is growing, when it is processed, or when it is served. Often when food poisoning occurs, it is nothing to do with the restaurant serving the food, but further back in the production process (eg meat contaminated at the slaughter house is more common than in the restaurant kitchen).