Mobile ethnography - tips from an expert

Yesterday, I read some thought-provoking tips from Ethnosnacker on how up-front researcher preparation can ensure quality data from a mobile ethnography project. As I plan a project to capture use and lifestyle data from participants over a one-month pilot period, I'm thinking about how to give participants specific tasks they can answer which will provide the research team with the kind of information we need. Because my main approach is observational interviews or contextual inquiry, I'm grateful for some advice on how to gather meaningful data without actually being there. An interesting conundrum for an anthropologist.