My dog has a spider bite. What should I do to help him right away?

Ouch. The area does look quite swollen and possibly already infected. Depending on the spider that bit Rocco, he may need antibiotics, steroids and antihistamines to prevent the skin from being necrotic (dying off) and systemic bacteria (bacteria floating in the bloodstream which can be life threatening) from developing. i would suggest cleaning it with Betadine diluted 50:50 with warm water for tonight if a vet visit is just absolutely not possible. This will help provide some topical antiseptic cleansing of the wound. Take special care not to get any of this in his eyes. Then getting Rocco seen by a vet first thing in the morning to get this area looked at and treated appropriately. However if a vet visit tonight is possible, then getting him seen right away is best, before it gets any worse. I hope everything works out well for your pet Rocco. Best wishes and take care.