Yes, Avast can create a Rescue Disk in case of emergency. To create such USB disk, go to Tools > Rescue Disk. At this point you have to choose between CD and USB. Click on USB, select the drive and that's it. Sit back and wait until the process is finished. To test it, reboot the system while the USB is attached to a USB port, and press the Boot Selection menu. If if doesn't appear in the list, expand Hard Disk (only for some BIOS manufacturers) and select it from there.
For more information I recommend checking the page created by Avast for this purpose: https://www.avast.com/faq.php?article=AVKB114
