First episode - so confused!

This experience is what people who have DID call "losing time", which is a dissociative fugue state. In your case it was brief. You came to the same day, not more than a few hours later. Lost time can be very brief, or can run much longer than that.

In DSM prior to DSM-5 dissociative fugue was a stand-alone diagnosis or a symptom of dissociative amnesia. In DSM-5 (published in 2013) fugue states are stated to be rare in dissociative amnesia and common in dissociative identity disorder.

Your experience is a fugue, not an amnesia, because after you came to you were not able to connect your purchasing first aid supplies with any explanatory evidence or event in your life. This suggests that some other part of you, a dissociated part, was following through on some experience of their own, perhaps related to something that happened years or decades ago, that you have forgotten or never experienced in the first place.

I know how confusing and scary this kind of experience can be because I have lose time myself. You and I are not alone. In fact, we have a lot of company! Most posters on the DID Forum can relate. And it is treatable with psychotherapy (talk therapy).