Should you eat this poptart before my track meet tomorrow because I run the 800?

No absolutely not, instead eat a piece of toast with jelly or a piece of fruit and a handful of nut.

You'll burn all the pop-tarts quick energy boost before your race and feel worse after because it is such an unhealthy food, the toast will give you more sustained energy with the jelly to give you a get up and go better then the poptart.