Bike helmets as tools for advocacy
Whether or not to wear bike helmets for casual riding/commuting is an evergreen discussion within cycling circles. Arguments include that it improves safety, that it doesn't actually make much of a difference (especially in collisions involving cars), or that wearing helmets encourages riskier behavior, both from the rider and drivers. Additionally, telling people that they should wear helmets (or shaming them!) can make biking seem unsafe, discouraging ridership. This is especially the case with mandatory helmet laws. Countries with high ridership tend to have a culture of not wearing helmets largely due to a mix of cycling not being seen as a sport and high safety at an infrastructure level. If you want an in-depth look at the arguments I recommend this video from Shifter. I personally wear a helmet for every ride, but have no interest in pushing or shaming others to do the same. All I recommend is to make sure your helmet fits well and to check that it's actually effective if you do choose to wear one.
The argument I propose is that helmets can also be a tool for advocating for better bike infrastructure and getting more people out of their cars. Several studies across different countries have shown that store owners and shoppers overestimate car use as opposed to other modes of transportation. This could be for a wide range of different reasons ranging from the store owners/employees driving at higher rates than customers, to complaining about parking being an easy topic for small-talk while also being a signifier that the customer drove. Carrying your bike helmet with you (or even wearing it in) is a strong signifier that you biked to the store and could start a conversation around that. Unlike other potential signifiers like pro-cycling pins or patches, a helmet indicates that you biked there for that trip, as opposed to just that you bike in general. This can help shift the store owner's perceptions, especially if it's something they see repeatedly, and could help move them towards being more receptive of cycling infrastructure improvements or installing bike racks in front of the store (at which point the bikes parked out front themselves become the signifiers).
Other shoppers seeing your bike or helmet could be a push towards them seeing cycling as a viable alternative to the car for their own errands, especially as e-bikes and e-bike subsidies become more common. I've had several conversations start by people seeing my e-bike while I'm locking it up and asking about how it works for me/where they can get one themselves.
Better cycling infrastructure is in the best interests of store owners, as bike lanes and other improvements have been shown to increase both consumer spending and customer counts, even if it requires removing some parking spots. The slower speeds and human scale of cycling encourages spontaneous stops, and can also make regular smaller trips an easier option compared to large, infrequent trips by car.
All this discussion does leave out modes of transportation outside of cycling such as walking and transit, but I still believe that they benefit from this advocacy. Reducing car-dependent design, improving bike and pedestrian paths, encouraging human-scale density, and less noise from cars are all things that everyone outside of private cars benefits from. Even drivers stand to benefit if car trips are reduced to those traveling long distances, carrying large/heavy loads, or otherwise actually requiring a car, then there will be more parking available even if some parking is removed to make space for improved bike and pedestrian infrastructure.
Ultimately, the helmet isn't what actually makes the difference here; rather it is a tool to shift perceptions and open conversations that lead to change. Every bike rack and bike lane is a step in the right direction, and more importantly, so is new every person in favor of these improvements. Hopefully with time more places will have the culture and infrastructure in place to make cycling safe enough that needing a helmet isn't even a question. In the meantime, you can use your helmet as a shopping basket for quick shopping trips.