Libre Office Calc offers an alternative to Excel for spreadsheets. This comes as part of the Libre Office suite, and if you can use an Excel spreadsheet, you can use Calc.
There’s also a presentation package called Impress, as an alternative to PowerPoint, and again, if you can use PowerPoint, you can use this one. Don’t worry about the hardware at the venue where you’re giving your presentation not being able to recognise the package – all programmes in the LibreOffice suite are fully compatible with just about anything – more so than Microsoft products.
Download Libre Office for free here.