Get a 1 Gb USB keychain drive, format it FAT32, and load on the essential programs you need in Win and Mac formats. Then plug and go on any USB equipped machine. Test this before leaving, of course. While Mac programs will generally run without installing System components, you may be faced with doing an Install on a Windows machine from your USB drive. (Windows tweakers please chip in with advice on how to have an independently running app from a removeabe drive)
Also, BBEdit for Mac allows you to edit files directly off an FTP site. This can be really handy. Especially if you construct your website with the variable content in Server Side Include files that are primarily text - you can update text content without monkeying with layout.
Or, investigate server side software with blogging type features, or Web based editing, or even email based updating.