Carry a reusable cup or sit in and drink from a ceramic one. Many cafes give a discount for bringing your own cup, and cup-return schemes are spreading in cities.
A United Nations Environment Programme (UNEP) review of life-cycle assessments (LCAs) found a reusable plastic or glass cup beats a plastic-lined paper cup with a plastic lid on climate after about 20 to 24 uses. Steel cups take more energy to make, so they take longer: about 130 uses in one study paid for by the paper-cup makers Huhtamaki and Stora Enso. The studies put a paper cup's plastic at about 4 g of plastic per drink, a 3 g polystyrene lid plus a 1 g polyethylene lining; a cup a day on working days is about 1 kg a year.
The catch: single-use compostable cups are not a fix, since most end up in landfill where they can emit methane, and only 28 percent of home-compostable items disappeared in University College London (UCL)'s real-world compost experiment.