Use prepared mayonnaise instead of making it from scratch, as the egg ingredient has been pasteurized and the additional lemon or white vinegar is acidic and has quite a bit of salt. All these ingredients help when paired with a low acid food such as potatoes.
Raw eggs are a possible safety hazard when left out, and can develop salmonella bacteria when left at room temperature. If adding sliced eggs, make sure they are hard boiled and therefore fully cooked. Temperature guidelines are important in warm weather, but also remember to start with clean utensils, bowls and ingredients, with no cross-contamination, especially from the cutting board when chopping the potatoes.
Once the salad is finished being prepared, chill in the refrigerator for several hours, four is ideal.
Pre-chill the cooler for the potato salad with cold water or ice before dumping and adding in the finished salad.
Bring along a larger bowl and make a nest of ice to place the bowl of potato salad into, keep it covered until service and remove once the buffet line has gone through (you can always place it out later for seconds). Also, it is important to keep the potato salad out of direct sunlight.