Watch your surroundings. When I enter a walmart I pay attention to loiters and people that seem to be out of place. Warm night with jackets or sweaters or roaming around, leaning on walls near front entrance casing people.
Once those are established you know who to potentially keep an eye on.
People asking for change or anything say no and keep walking. I dont allow them to close the distance. They want to read your body language, what your carrying, and if you take your wallet out its a chance of snatching or worse when your distracted and looking down they attack. A local person in my area got his car stolen when picking up his kid at school. A man approached him while he was waiting in his car picking up his son. Man ask what time it was, guy looks down at watch, looks up gun in his face. So don't get distracted.
Have a pepper spray or taser in pocket ready to go. If it makes you more comfortable have it in your hands. Since you parked further your at a good start to be able to see if someone is following you. When loading your car and someone approaches, ask what they want before they get too close. Usually you can tell, depending how good you are at reading people on their intentions. Tone of voice, body language etc.
If you act scared they know your scared and prey on you. When your confident well aware of your surrounding they know your not an easy target and wait for someone easier Stay alert.
May have grammar/spelling error. Typing on phone