Norton Power Eraser and Hitman.Pro are good portable on-demand scanners. You can also use AdwCleaner to remove PUP or preinstalled programs. Process Explorer and Autoruns can be quite useful if you activate the VirusTotal checking.
That are all tools I know and that I personally use for malware checking and cleanup. All I named can be used from a flash drive
RogueKiller is a security tool that can be used to terminate and remove malicious processes and programs from your computer. RogueKiller has the ability to remove infections such as ZeroAccess, TDSS, rogue anti-spyware programs, and Ransomwares.
I've used both Norton and RogueKiller and they're both excellent on-demands. However, I think neither one is portable. Both write into the registry. HitmanPro on the other hand is fully portable, using a proprietary folder for its settings and logs. I do believe RogueKiller has a commandline scanner, like Emisoft. Emsisoft's Kit installer also is not portable.
Edit: corrected, Norton Power Eraser is a portable software.
microsoft safety scanner (the defender scan without having defender). crystal (uploads to virustotal) , emsisoft emergency kit. malwarebytes antirootkit (only checks for specific things). mcafee stinger (only checks for specific things)