Hey guys, I've been watching the progression of things on this thread with interest. Looking good, so far.
For just listening purposes mp3 files are fine.
Formats normally used for sharing 'mix ready' files are Wave (uncompressed), FLAC (lossless compressed) or AIFF (Apple equivalent to Wave). Any half decent DAW will accept these formats. I wouldn't try to use the Reaper files, since they are probably 'chunks' of sound file, used in your mix and of doubtful use to anyone else.
In the DAW I use, Sonar 8 Producer, I simply solo the track I want and export it, primarily as a Wave. From there, I can easily convert to any other format I need with Audacity (the mp3 codec should be easily located).
I'll, normally, send out mp3s just for reference and to present ideas. If all is good, I'll send Wave files.
Like many other DAWS, I can export the whole mix in a folder, files, settings, audio chunks, waves, etc. But it is an enormous folder of files, only useful if you have Sonar 8 Pro....... and a spare drive to carry it...LOL.
Just for fun, here is 'Freestyle' with a bass I put onto it way back in January. I gotta confess, this isn't my favourite style, LOL. I sure had sore fingers after about the 6th take.....
If you guys need someone to put this mix together for ya, give me a shout. I've gotten more and more interested in mixing/producing over the last couple of years and the practice will do me good.