The standard RPG 7-dice set includes all of the standard die, specifically the following:

• 4-sided die (d4) 
• 6-sided die (d6) 
• 8-sided die (d8) 
• 10-sided die (d10) 
• 10-sided percentile die (d%)
• 12-sided die (d12) 
• 20-sided die (d20) 

These RPG dice are the staple of the tabletop gaming world. The 7-dice set contains all varieties of dice necessary for DnD, Pathfinder, Earthdawn, Call of Cthulhu, and more. However, each set contains only one of each die. Many players prefer to have several. That way, when your wizard is launching three darts of Magic Missile at a target, you can roll 3d4 at once rather than rolling a single d4 three separate times. 

There are several solutions for building up these larger dice pools. You could purchase packs of d6s or d10s or you could purchase multiples of each die individually. But by for the most common solution is purchasing multiple different 7-dice sets. People acquire different sets for different characters, campaigns, and occasions; for larger dice pools; and simply because the new one looks so cool or the old one rolled too low too often. 

Then there's always the killer Pound o' Dice solution: just get yourself a mass of different dice in a chaotic variety of colors and fonts to fit all the gaming occasions where a handful of sets just isn't satisfying enough. 

Of course, here at Awesome Dice our preferred solution is all of the above. As a team of dice goblins, we generally believe no one person can ever have enough shiny math rocks.