My budget travel practice changed completely when I started tracking every expense in a spreadsheet. This is what I learned from 3 years of data.

The categories that were higher than I expected: transport (not flights — local transport, taxis, tuk-tuks, ferries add up), activities and entrance fees (especially in Europe), and drinks (alcohol specifically, even at low prices in cheap destinations).

The categories that were lower than expected: accommodation (I'm better at finding deals than I thought), food (street food discipline works), and clothing/gear (I buy almost nothing while traveling).

The most useful insight: variance matters more than average. On a $35/day target, having a $60 day followed by a $10 day is fine if your weekly average is on track. Budgeting weekly rather than daily removes the anxiety of individual expensive days.

The spreadsheet setup I use: one row per day, columns for accommodation, food, transport, activities, and miscellaneous. Running total column, daily average column. Takes about 3 minutes per day to fill in. The pattern-finding after a month of data is genuinely illuminating.

The single most useful thing the spreadsheet showed me: I was spending significantly more on café coffee and drinks than I realized. Not because any individual purchase was expensive, but because of frequency. That data changed my behavior without requiring any willpower — I just needed to see it.