Since afaik plugins are not yet supported, there is no way of using all those fancy MySQL plugins made for SA-MP, so you're left with storing data in plan text files. For that purpose, you should use the functions from file.inc. Open data stream with fopen, write the stuff you need with fwrite and close the stream with fclose. You can then access the stored data by using fread (don't forget to open and close the stream too).