Cross-platform portability and byte ordering tips, tricks, best practices, gotchas, pitfalls, and stumbling blocks?

[Yet Another Troll]

Is anyone out there doing portable complex programs on all or most platforms supported by xbasic? Which platforms allow OPENW w% where w% > 1? Has the RANDOM bug bitten you in Win32? How do you deal with differing endianness and other byte ordering issues in memory, binary data files, and TCP/IP? Data storage issues on Android because even empty, freshly formatted SD cards are mounted read only, while the RaspPi is simply not the boss of you like that? (Do I read the db off the SD, cache CUDs to the internal storage, and sync with a distributed db server over TCP until updated SD cards can be physically distributed and slotted in?) What worked here but not there? What got you good, and how did you work around it?