The older population is particularly susceptible to malnutrition, which currently affects 1.3 million people aged 65+ in the United Kingdom. Malnutrition is an outcome of food insecurity and despite demographic changes that have led to a rise in numbers of older people, we know very little about how older people become vulnerable to food insecurity. The aim of this study was therefore to explore older people's everyday food practices in order to expose the strengths and challenges within local and national food systems, and better understand how food insecurity might arise in later life. This empirical study operationalised practice theory using a multi-method ethnographic approach with 25 households aged 60–94 years, comprising interviews, observation, visual methods and food logs. A model of vulnerability developed by Schröder-Butterfill and Marianti framed data collection and analysis. Analysis revealed the assets and adaptations older households used to protect themselves from threats to food security. Factors ranging from changes to physical and mental health, and structural factors such as supermarket design, moved households towards food insecurity. Smaller everyday ‘trivia’, e.g. lack of seating and accessible toilets in supermarkets, accumulated to shift people towards vulnerability. Vulnerability is structured by the habitus but is a fluid, relational, temporal and socially constructed state, and people moved towards and away from vulnerability. We have developed a model that accommodates this fluidity, incorporates the concept of ‘cumulative trivia’ and suggests how the ‘aggregation of marginal gains’ could counter-balance and address trivial threats. This model demonstrates to policy makers and those working in public health how vulnerability to food insecurity operates and where interventions could be applied to support households to achieve food security and avoid becoming malnourished.