The MiSTer menu can be customized in a number of ways.
eg You can add a cool font, or change the background image for the main menu.
To change the default font
Create a /media/fat/fonts folder on your SD card.
Next download the fonts from here - MiSTer Fonts
Copy the pf files downloaded from that url to the /media/fat/fonts folder
Next edit /media/fat/MiSTer.ini
font= line, and edit to use a new font. Be careful not to add a / before the font folder!
If you want to use the C64 font - change the font line to
To add a background image
Find a suitable png or jpg file that you like
Copy your desired image to /media/fat/menu.jpg or /media/fat/menu.png (as appropriate)
Press F1 once rebooted into MiSTer to select your background.