I have several Boot CD's/DVD's where I'm able to make a bootable USB-stick and put into it. But I can do this separately only. Is it possible to merge several bootable CD's/DVD's into a single bootable USB-stick where I can choose which system to boot from? I'll be happy for a good link, or if you just tell me the steps with the right expressions that i can google.
Yes this is possible, try out a great application called Yumi it allows you to make a long boot list with an iso if you have it, you can even use unsupported bootable iso's to be included.
This possible using a bootloader like grub - or if you are working with Windows grub4dos
In the config file you can add multiple ISO images you can select from in the boot menu.
Alternatively if you prefer a clean hardware sulution take a look onto the ISOStick - an USB stick that includes an hardware emulated usb cd/dvd-drive booting from an ISO contained on the stick.