What kind of boot card is needed if want to power up camera directly to CHDK mode without physically touching the camera? SX260HS or S110 is controlled by CHDK PTP.
On these cameras, any card with CHDK installed formatted FAT16 or FAT32 with the BOOTDISK will load CHDK at startup.
Not clear what you mean by "CHDK mode" but if you need to perform additional actions after startup, you can use a startup script.