Does the seller have to hand over supplier and customer contact lists on closing day itself?

Only if the purchase agreement actually says so. Contact lists, customer databases, and similar business records are commonly included among the purchased assets in an asset sale, or simply come along automatically as part of the corporation in a share sale, but whether the seller is required to physically deliver them specifically on closing day, versus sometime during an agreed transition period afterward, comes down entirely to what the agreement specifies as a closing deliverable.

If having this information in hand right at closing matters to you — and for many buyers it genuinely does, since it's central to actually running the business the next day — make sure it's listed as an express closing deliverable in the purchase agreement itself, rather than assuming it will simply be handed over informally because it seems obvious. Sellers, for their part, should confirm exactly what they're contractually required to deliver and when, so there's no dispute after the fact about whether an informal expectation was actually a binding obligation.