What Does It Cost to Pack for a Flight Under the Carry-On Liquid Rules? Container Limits, Travel-Size Price Premiums, Toiletry Price Indexes 1935–2025, Travel CPAP Devices and Compression Stockings, from Regulations, Retail Prices, BLS CPI, CMS Fee Schedules and TSA Counts

Air passengers in the United States, Canada, the United Kingdom and the European Union may carry liquids in containers of at most 100 ml (3.4 US fluid ounces) in one bag of about one litre, a rule that shapes what travellers buy and pack. We document the rule and its exemptions from official sources and describe the costs around it. On one US retailer's shelf on 25 September 2026, 10 of 16 travel-size toiletries cost USD 1.99 or less, but their price per ounce ranged 6.41-fold, from USD 0.59 to USD 3.78. For four products sold in the same version at two sizes, the travel size cost 1.09 to 3.01 times as much per ounce as the full size, the maximum for a 3.2-ounce mouthwash against a 1-litre bottle. The consumer price index for personal care products rose 8.18-fold from 1935 to 2025 and 12.0% from 2019 to 2025, against 25.9% for all items. Travel CPAP machines listed at USD 769 to USD 1,149; the USD 769 and USD 919 models cost 1.44 and 1.72 times the USD 534.45 that 13 months of Medicare rental amount to at the July 2026 median fee; that fee fell 62.8% between 2015 and 2017. In pooled trials of passengers on flights of more than five hours, symptomless deep vein thrombosis occurred in 3 passengers wearing compression stockings and 47 without, with trial pressures of 12–32 mmHg. US checkpoints screened a record 906.7 million people in 2025. All inputs are public; the retail and device prices are commercial single-day observations.