Be more organised, stop expecting everything to handed to you on a plate. I don't mind though, it subsidises those of us who do think ahead. Again, it isn't a month - very cheap fares a month in advance, cheaper fares up to a week (and often a few days if you travel at certain times).
You're quite right about making fair cost comparisons between rail and air. People do seem to deliberately forget that booking ahead can save you money on the trains in the same way as the airlines - and there is an annoying habit of comparing advance booked air fares with walk-up rail fares.
However - I do feel quite strongly that as a matter of principle, walk-up rail fares should be affordable. It is more and more the case that when, for example, the government is challenged about the cost of rail travel, they point to the advance fares as examples to say that it is not expensive.
This I find unacceptable because rail isn't just competing with air, but with the private car. I am completely in favour of eliminating domestic air travel where there is a rail alternative, but I actually think that reducing car dependancy is probably more important. The benefits of that are not just environmental but social.
Therefore - if we are to agree that reducing car dependancy is a worthwhile aim (sadly current transport policy doesn't convince me that this is a priority for the government) - it is essential that the cost of rail travel is comparable to the cost of going by car. This is where the principle of walk-up fares comes in because if you are going by car you don't have to plan the exact time you travel a month in advance. You might decide you are going on a certain day, a couple of weeks beforehand, but you don't commit yourself to a particular time (or even a particular route). Advance rail tickets, on the other hand, don't allow you this flexibility - and it is that flexibility that inevitably makes many people choose to travel by car instead of public transport, especially when the cost is less, or equivalent.
People are saying it's unreasonable to expect to be able to go to Glasgow at a day's notice. I disagree. Car drivers have this option, but anyone dependant on public transport doesn't. It's not often that I decide to do a long journey that spontaneously - but that's not really the point. It might be that I want to travel up on a Friday afternoon, and I don't know what time I will get away from work until the day. If I have to book in advance, I will have to book the latest train of the day just in case I can't get away till then. Then I might be done with work early and am then sat around waiting pointlessly for several hours. My counterpart in the car-owner's parallel universe, meanwhile, has set off when it suited him.
Or - and this is something I do quite often - I have spent a week in the north of Scotland and I have a ticket back to London, but I want to stop off in Glasgow to see some friends there. But I want to be able to change my plans at the last minute because if the weather is amazing I might stay up north for an extra day, or if it's crap I'll decide to head south a bit earlier and have more time in Glasgow. None of this is life-critical stuff but the point is that it is a significant factor in many people's decisions about which mode of transport to use.
I don't expect total freedom - I understand the reasons for making peak time travel more expensive - I just think it's reasonable to expect to be able to walk up, on the day, and buy a ticket that lets you choose between several different trains without penalty, and which is priced at a level that means it is at the very most, equivalent to one person making that journey by car. (Ideally, it should be equivalent to the cost per person of three or four people travelling by car, because it is that point at which the energy efficiency of each mode of transport starts to become similar).
This includes being offered a ticket which allows me to easily understand which services it is and isn't valid on. This is not the case at the moment, despite the "simpler fares" propaganda we have been given recently but is largely a failure (I have ranted at length about this on here before - and a recent parliamentary committee agrees with me).
On the wider issue of High Speed Rail vs. investment in local and medium-distance public transport; I'm inclined to agree with the other comments on this thread that the latter is possibly more important. It would be nice to have both of course, but improving local bus services and reconnecting station-less towns seem to offer the greater benefit. There are very few domestic journeys which really need to be done by air so I'd rather tax the majority of domestic flights out of existence and spend the money on transport improvements that will benefit those at the bottom of the pile, before embarking on HS projects that will shave 30 mins of a journey here and there. As far as I'm concerned there's really no justification for flying from London to Edinburgh/Glasgow or anything shorter than that at the moment - whether there's an HSR alternative or not.