Any command with set-uid, or set gid-bit, set. Will be run as the owning user or group. However if they are written properly, they will not let you do anything that you should not.
su only allow you to do anything of significance if you provide the correct password. Most other tools will just do one thing safely, but not allow you to escalate privileges.
However if you can write to the storage, as root (by removing media, and inserting into another machine, or booting into a different OS), then you can add the files that you need, with the appropriate permission.
Executables with set-uid/set-gid bits, are the only way of escalating privilege in Unix systems (The modern systems now have capabilities, but these amount to the same thing).
The kernel does not use passwords, so to implement passwords, an executable with root owner and set-uid bit set, is created. This executable will check the password, and then set the user appropriately, and start a shell (or something).
Supposing there is no use of capabilities, then
find / -executable -type f -user root -perm -u+s -print 2>/dev/null will list all executables that elevate permission (at least temporarily), most (maybe all) will be useless.