Table size varies for each Regional location. While there is no way to know in advance the exact dimensions of the tables your teams will be assigned, you can plan for tables to be:
between 5′ to 8′ in length
between 2′ and 3′ in width
unadorned
How you utilize your presentation space is left up to each team. Some choose to bring a table cloth (often schools have one with their school or district logo). All of these choices are left to the individual teams to determine.