A pottle, technically speaking, is a unit of volume equal to 2 quarts or ½ gallon (see The London Adviser and Guide, for example).

The word “pottle” is also used to describe a sort of conical basket used to carry produce – often strawberries or other small fruits – as they are sold in markets or by street vendors. The Universal Gardener and Botanist (1778) provides a description:

Pottle baſkets are the moſt convenient for ſending quantities of ſtrawberries, raſpberries, and mulberries, choicer ſorts of early cherries, and the moſt delicate ſorts of ſmall plums, to market, or to any diſtance; theſe are very ſmall, upright, chip Baſkets, holding about a quart, being ten or twelve inches deep, very narrow at bottom, and not more than four or five inches wide at top, where there is a croſs handle. The London gardeners uſe vaſt quantities of them, buy them at ninepence or a ſhilling per dozen, which when filled with fruit, they pack many together in a large Boat-baſket, ſo ſend them to market on men’s heads, or otherwiſe.

The Museum of London describes their use in the early 19th century:

Strawberries were cried by both men and women in June in London suburbs. They were sold for sixpence in pottles that held less than a quart. The crier added one penny to the selling price for the value of the pottle that was refunded if the customer returned it. The criers’ profit was between threepence and fourpence in the shilling.