The offence carries a maximum penalty of a fine of £1,000 and/or 3 months custody.
Magistrates’ sentencing guidelines suggest a “starting point” of a fine of one and a half week’s net income (reduced by a third for a guilty plea). From your description of events I see no reason for them to depart wildly from that guideline and, in view of the small amount of alcohol involved, they may see fit to reduce it a little. In fact, in view of your good character (the 1999 offence is too old for consideration) they may even feel inclined to deal with the matter by way of a Conditional Discharge. You will also have to pay prosecutions costs (probably about £85) and a Victim Surcharge of £15.
Although a banning order is a possibility, these should only be made where the court is “satisfied that there are reasonable grounds to believe that making a banning order would help to prevent violence or disorder”. From your description it seems they would be hard pressed to identify such grounds. You could relate your “92” exploits to them to help dissuade them from making an order if they are thinking of doing so. The Duty Solicitor scheme should be available to you. It is now only available to defendants for their first appearance only and who appear on bail (which you do) and who are charged with an offence that carries a custodial sentence (which you have been).