Let's say you tested negative for a food allergy on both the IgG and IgE tests. What is the likelihood that you are actually allergic to the item?

Depends. Having igg to a food merely means that you have been exposed to that food and in fact the igg4 (a subclass of igg) may even indicate that you can tolerate that food. The presence of ige to a food alone does not necessarily mean that you are allergic to it. Usually it takes a much higher value above the normal to get a positive response when challenged.