You won't ruin any of your devices by plugging too many of them into a single outlet (assuming you don't start a fire by bypassing overcurrent protection mechanisms - like the old trick of screwing a penny underneath a fuse). Electricity simply doesn't work that way.
If you're so worried about what might happen, educate yourself, first by learning the basics of how electricity works (maybe your local library is a good place to start) and then by obtaining simple test equipment to see what is actually happening in your home. The Kill-A-Watt line of products have a well-deserved reputation for providing easy to read information about what is actually passing through your outlets.
Once you start educating yourself, you'll learn that when it comes to alternating current (aka household electricity), 15 Amps at 120 Volts doesn't always equal 1800 Watts as it would in the case of direct current, thanks to the interactions between capacitance, inductance, and resistance. Power socket meters, like the Kill-A-Watt, can make these distinctions quite clear and easier to understand.