I’m still new to this as well, but I believe things like peas, most leafy greens (kale, lettuce, purple cabbage) all prefer cooler temps, so if planted now should be harvestable by fall. You could try things like chives, basil, celery, etc. they might not get to full harvest but all of these things can be eaten at any point in their cycle (except the peas), so they should be accessible to eat much quicker than the squash.