The RPT file contains the sizes for the drills located in DRL file.
The .1 .3 .S1 .S3 .SM1 .SM3 .SP1 and .SP3 and .GND files are Gerber files, and the USR file contains the mappings from D?? tools to pad sizes and line sizes. Surely should be distributed between cooper, solder mask, silk layers, ground cooper and I cannot figure right now the other.
The .XY file marks the positions for auto-mounting the pieces.