Perhaps you by yourself won't make a difference, but I do the same. I won't send a dime in Illinois, the only thing I leave there is trash and bodily waste.When I drive through Illinois I do not stop at all, except for a bathroom breaks (a couple of times made it through without having to urinate) in the last 20 years. Illinois does not allow firearms outside your vehicle if traveling, and not spending money so that they get tax dollars on is the guiding principal. I realistically know that it isn't going to make a difference.
I have cousins that do the same.
There may be more folks "boycotting" Illinois than some realize.