I have done my fair share of networking and event attendance over the last couple of years with M Communications. I have to be honest ... I am guilty with forgetting an item below on occasion. (This is usually is when and event is at 7 a.m.) Me no likey. Anyway, here is the list.
Business cards and pen. Now I know this seems super-duper obvious, but I have heard "I forgot my business cards" more often than not. I have also been asked by other people if they could take one of my cards, write their contact info on the back to give to someone else. Business cards are not the most expensive marketing materials, but they are marketing materials nevertheless. My point? Don't do this. The same goes for pens ... borrow and give back.
Cash and receipt books. If you are selling product, you need to have both of these bad boys. Period. I know this also seems pretty straightforward, but if you are in the last minute pack up your booth mode, it can be pretty easy to forget. My advice? Pack the night before.
A good attitude. The message here is simple ... if you are having a bad day stay home. Do not attempt to do conference calls either. Cranky comes across equally the same, whether it be phone or in person. People tend to gravitate and want to do business with positive and happy.