The happier and more relaxed you are, the less likely you are to strain your throat. Have a quiet reflective pint, and sup it slowly about half an hour before you go on - that should let you get rid of most of the liquid excess before you go on. Warm up your voice gently before you go on. Sing a gentle song if you have one that doesn't evoke bad emotion.
Remember that when you go on stage, the nature of most audiences, in our game at least, is that they want to enjoy your performance, to join in singing with you, to listen to your songs, voice and art. They generally want to identify with you as part of a cracking evening.
When I sing, I try to keep my head fairly level or slightly raised - I DON'T throw my head back as this reduces support for the vocal cords. Simple posture is to pull my bum in to avoid hollowing my back for the same reason (that reason, and that I am vain and not proud of my beer belly). I keep to the key I have rehearsed for the song and I try not to be tempted to push the pitch up to gain extra volume as this is the major thing that leads to voice strain - if I find myself doing this, I just remember how many nervous pub singers I have heard do this and with what result. I am not ashamed to use a pitch pipe, nor to consult a song list, but if you use one, make it large enough print that you can see it on the floor at your feet.
One of the things that I find if I don't use a pitch pipe is that I tend to start the next song in the same key as the previous one, because it's still ringing in my ears... and if I do pitch something wrongly (it happens, despite the precautions), I stop the song emphatically and wave my hands around, with comments about the durability of my truss, upsetting the bats in the rafters, or whatever, then I start from scratch, pitch pipe again, and I do take two. This is a major reason for being sober - if you have been supping all night this is hard to do.
I watch a previous act because it tells me what the audience is up to. If the audience is noisy and fragmented, I will start with something like "Flying Fish Sailor", but at a normal volume, because everyone knows the "Blow the Man Down" chorus, and it tends to seep out through the layers; I can see how far it gets, and can judge the next song accordingly.
But that's all about me and a little bit of how I work it for me. I tried to make it as much like it is for me as I could, in the sincere help that it will help you Paul.
In terms of drinks, I have a slow pint before, I have a small port and brandy on hand in each set, along with a pint of water at room temperature, with lots of lemon or orange slices in it... and I sip the port, only if I need it, and usually it lasts me for both sets, and the water I only take about 10mL at a time between each song and hold it in my mouth to refresh before I swallow.
In my interval, I get some fresh air and another quietly reflective pint. I like to think that I would avoid gratuitous sex at this stage of my performance, but as it has not happened yet, and I think it is never really likely to be an issue with me, (if it ever did, what second set?), I tend to refuse drinks (full pint), and to disengage from "do you know ..." conversations fairly quickly.
I have gone into a great deal of detail here, but on re-reading it doesn't seem to describe my philosophy. I guess you would have to be me to follow this crap, but if you can get any help at all from this, I will be glad to have helped.
PS If you are Paul/Modern Triumph/Middle Bar, and recognise Borneo, please e-mail me on email@example.com, as I would love to hear from you.