I have set up a keybased SSH login on my server. Now when I am not in the office and don't have my key with me, there is no option for me to access my server. Going back to password-based logins is not an option for me.
What is the best practice in this case so that I can use SSH without my key occasionally?
Best practice would be to continue only allowing key based logins, and just put up with being locked out when you are without your key.
I am sure there is some way of reconfiguring your sshd config to allow password logins, but how are you going to secure that? Your security is only as good as its weakest link.
There isn't really a "best practice" option between allowing password logins and private key authentication. You have to choose whichever one is most acceptable for you, and just take the problems that come with either on the chin...