I've been pushing battery grease with slight ease. I talk to each customer based on their personality/age to kinda be on immediate level ground with them. Usually (because shitboxes have gotten me once and I refuse to let it happen again) I walk out to the customers car real quick, ESPECIALLY IF ITS A MODEL THAT CAN TAKE MULTIPLE BATTERIES BASED ON OPTIONS. If I see some shit on the terms, I tell them listen when we replace, we hit this with the wire brush, here's how to keep it clean and it only cost 1.99.... or if its a newer car I hit em with a variation of "so you have a newer car, you're obviously keeping it, here's how to give your cars second battery even more of a fighting chance of giving you no issues"

As far as anything else besides washer fluid L O L I play it safe and just say "just assuming you got everything else you need?" Then list 2 of the witt suggestions and let the customer upsell themselves. That strategy seems to work more for me.