You'll want/need Verbatim "Data-Life" as the Azo Dye is dark enough for the laser to read it with minimal read errors... trayloader iMac G3s used similar CD-ROM drives as the Wall Street/Lombard.
Don't waste time burning CMC Magnetics media(store brand/Memorex/etc) or retail store Verbatim CD-R(rebranded CMC Magnetics/India Moser-Baer) as the dye is too thin for the laser to read it.
CDRW media will work on 90s era Macs, it still comes down to who the maker is and quality. I've had good luck using Philips, Imation, Verbatim CDRW media on older Macs but as the media ages the re-writes/skin oils on the upper layer(label area) will make them more unstable over time.
...since all PowerBook G3s have a PCMCIA slot, you can still buy a low-cost USB/USB 2.0 card at a reasonable price and use a flash drive for shuffling files.