Here is what I do:
Type in all kinds of passwords in an excel file (.xlsx)
Zip it with a password by 7-zip
length > 8
combination of A-Z a-z 0-9 symbols
different from any other password
Upload it to Dropbox or so.
Is it safe enough, as I do not want to install any additional software specifically for storing passwords? (I mean, if I insist no additional software, any safer ways?)
Be a little bit more specific:
Basically I guess no one will be interested in my passwords. Is it safe enough to prevent some casual attacks (for fun maybe) by hackers?
If the government is interested in me, and my computer may be taken, is it safe?
The guy asking this question is paranoid and quite lazy (to install additional software).
KeePass is recommended by pepoluan in case I am not that lazy. An extended list for password management can be found in a related question on this site: How do you keep track of all your passwords?, in which KeePass is the top voted.
The question is still open to better answers. No extra password-/encryption-specific software.