Switch body wash, shampoo and conditioner to bars, and hand soap to a bar in a dish. Buy them loose or in paper, and keep them dry between uses so they last.
A bottle of shampoo or shower gel uses around 40 g of HDPE; someone getting through a dozen bottles a year avoids roughly 500 g. Lush reports that 37 million naked products a year, 58 percent of its units, have avoided more than 15,000 tonnes of plastic since 2005.
The catch: some bars are wrapped in plastic film or sold in plastic tins; check before you buy, and give your hair a couple of weeks to adjust to a shampoo bar.