Not spesifically a tool to put on a USB stick, but Ventoy is worth checking. I’ve had a bit mixed results with it on older hardware but when it works it’s pretty easy to manage your carry-on-tools.

UNetbootin could be cool, it’ll provide access to mamy iso’s instead of just one.

Distro’s supported:

- Ubuntu
- Kubuntu
- Xubuntu
- Lubuntu
- Debian
- openSUSE
- Arch Linux
- Damn Small Linux
- SliTaz
- Linux Mint
- Zenwalk
- Slax
- Elive
- CentOS
- FreeBSD
- NetBSD
- 3CX
- Fedora
- PCLinuxOS
- Sabayon Linux
- Gentoo
- MEPIS
- LinuxConsole
- Frugalware Linux
- xPUD
- Puppy Linux

It can be used to load various system utilities too, such as:

- Parted Magic
- SystemRescueCD
- Super Grub Disk
- Dr.Web Antivirus
- F-Secure Rescue CD
- Kaspersky Rescue Disk
- Backtrack
- Ophcrack
- NTPasswd
- Gujin
- Smart Boot Manager
- FreeDOS

Testdisk, clamxTK, rkhunter or chkrootkit, mobile verification toolkit, lshw, time shift maybe deja-dup.

I think your idea is a good one. Like a linux Swiss Army knife. You can have lots of tools that you don’t need all the time but might be handy in a pinch. Especially if you don’t have internet.

Medicat

Hiren’s boot disk is the only answer to this question. I heard they updated it a few years ago.