Vole Office Ultimate is a portable app taking up ~225MB of disk space. I was surprised at first, starting this light weight app, since you're presented with what seems to be a blank screen -- click one of the headings to start the word processor etc. Depending on what you're after, it's workable, though if you're expecting a full-tilt office suite you'll be disappointed. The online Google Docs is of course one alternative, as is the open source LibreOffice, which also comes in a portable version, though the latest version is currently not available as a portable app. There's also a new release of SoftMaker FreeOffice available, which like the regular LibreOffice is a full installation with multiple folders, lots of new registry entries etc. You can however choose to install just one or two of the included office apps during the install routine.
libreoffice[.]org/download/download-libreoffice/
libreoffice[.]org/download/portable-versions/
neowin[.]net/software/softmaker-freeoffice-2024-rev-f1224/