On problems with no input, the stack has [] on it, which can be useful. For example start your program with 1+ instead of [1], or !2 instead of 1 2.
It's okay to have trailing newlines in the output, so n+ is often a viable alternative to ''+.
code.golf encodes your submission as UTF-8, but GolfScript is not Unicode-aware. Bytes 128-255 are treated as individual identifiers in code. This means 2:µ;¶¶+ prints 4. Remark that µ is c2 b5 and ¶ is c2 b6 in UTF-8. We are really assigning to c2, and both b5 and b6 are ignored (as undefined variables are).
[]+""+ converts a byte to a string of one character.