You could append every first word to an empty register (let's say q ) using

:'<,'>norm! "Qyiw

That is, in every line of the visual selection, execute the "Qyiw sequence of normal commands to append (the first) "inner word" to the q register.

You need to have > in cpoptions for the newline to be added in between yanks ( :set cpoptions+=> ), otherwise the words will be concatenated on a single line.

If you want to quickly empty a register you can use qqq in normal mode (or qaq to empty register a ).