Not sexy by any means, but spreadsheets are no-fuss and allow for the flexibility of including all the nitty gritty details of trip-planning, budget calculations, and tweaking things on the fly.
Pro Organizing data using spreadsheets can help organize ideas
One trick to game design is organizing ideas. Spreadsheet is very useful as i is very simple and limited cell based space but with ability to use mathematical formulas for calculations. Incredibly useful tool for building game rules.