The bill and its GST
A numbered GST bill per outlet with HSN codes per line, the slab per dish, and service charge that is taxable because the law says so.
A restaurant bill is a tax document. It carries the outlet's GSTIN, a number from the outlet's own series, one line per item with its HSN code and slab, the service charge if the outlet levies one, and the CGST/SGST split.
Tax groups
An outlet sets its GST groups once — food at one slab, liquor at another, packaged goods at a third — and each dish belongs to a group. A dish that changes slab is moved once; every bill after that is right.
Service charge
A service charge is taxable. The bill applies the outlet's rate and taxes it, and the steward's share is a fact the day-end report carries.
Numbering
Bills are numbered per outlet, per financial year, never reused. A reversed bill keeps its number and is marked reversed; the reversal is a document of its own.
The bill prints on the outlet's own paper — logo, address, GSTIN, footer — set once in the outlet's details.