Kantar forecasts the online share of FMCG sales in the US will rise to 5.4% by 2021, or $59 billion. Channel share is also starting to tip in the direction of convenience stores and discounters like Aldi, with this growth coming at the expense of traditional supermarkets.
Nielsen values the US FMCG market (including fresh food) at just over $1 trillion, up nearly 3.5% year over year as of May 2018. Ecommerce is responsible for much of that growth (82%), and nonfood items make up 87% of ecommerce dollars. This reflects the small amount of online groceries bought in the US.
So, what do the 57% of US internet users who've ever bought food online actually buy? According to Nielsen, 42% of consumers have purchased snacks online at some point, making it the biggest category. In 2017, online sales of salty snacks reached $207 million (out of $1.14 billion total). And while online sales of wholesome snacks were lower ($149 million), that figure represented nearly 43% of total sales in that category. Nielsen did not define "wholesome," but it's fair to assume there are a lot of power bars and jerky being bought online (nuts are a separate category).
In "The eMarketer Ecommerce Insights Report," conducted in June 2018 by Bizrate Insights, among the 36.4% of US internet users who had bought a grocery product online in the past month, slightly more bought dry food goods (21.4%) than snacks (20.5%). But respondents ages 30 to 49 purchased things like candy and chips online more than they did pasta and beans.