Where i can get a copy of dos that can be booted from a pen drive/USB? topic

Hello, i have a 2 GB pen drive and i wanted to put a copy of dos of it that is bootable so i can make a iso of it to then customize my own contents.
Also, will it be working fully if i just put batch files there and then boot from the usb to get there? And where would be the name of the batch file so i dont get a "Operating System not found" or a blinking underscore.


Any help?