Introduction
I've never went to a store or what have you to use public wifi. It's always seemed counter intuitive to me to expose yourself out in public when doing such sensitive matters.
Windows: A lot of Tim Horton's are like this, nowhere is safe huge windows or facing the rest of the public. Lots of reflections and angles can open up so it's imperative to choose your location wisely. Would also enable easy monitoring for LE from a far.
Cameras: Make sure you park far away or not drive at all, parking in the lot gives them a chance to spot your license plate on camera. Make sure you pick a different location often and as an added note obviously never use debit/credit at these locations and dress normally.
Monitored Connection: It's not like businesses want this sort of attention. Eventually they will start monitoring their networks for tor usage, it's also how pedophiles do their thing. If LE came to them to monitor their connection for a certain customer suspected of tor they would be inclined to cooperate. These connections can also be hotbeds for malicious actors spoofing the network to get passwords, if somebody finds out your using tor they may attempt to blackmail you or steal your package. With the amount of money going on and how easy bitcoin is to hide you're gunna start seeing more IRL malicious actors.
Possible Solution
Kali Linux: Use somebody else's wifi, comes with all the risk you would think and the fact you may be implicating somebody else. You're also committing extra crimes.
Long Range Antennas: Can be pretty pricey in some cases but it all depends how close you live to a possible source. It's possible to get smaller ones that are easy to power which will allow you to park further away from potential sources. As u/samwhiskey said it's possible to make you're own antenna. u/b00mtown_Vendor Says the Yagi antennae gets some sick range, 1mile+ with line of sight. Another user PM'd me suggesting a Alfa 1000mw antenna.
Personally I just use my own. I understand the risks of compromised sites but think it's minimal in comparison.
I use one of these bad boys. I can pickup wifi from 500 miles away.