A couple of further points:
1. If you
must book close to the date to travel, then you can sometimes save by splitting your advance tickets at Doncaster, or York, or York and Newark. Doncaster usually provides the best savings: to take tomorrow for example, your cheapest option to Newcastle (other than on the 22:00 departure) is the £54.85 super-off peak single. By contrast you can do it for £39 by taking the 11:48 Hull Trains service to Doncaster (£20 advance) then the 14:19 Cross Country train from Doncaster to Newcastle (£19 advance). The catch is that you have to spend just short of an hour at Doncaster station. Whether or not that is worth the while probably depends on your financial situation! Usually, to be honest with you, the savings aren't that high and its not worth the changing of trains and added waiting, but my example shows it can be done.
2. It's worth being aware of
Grand Central's train service to Sunderland. They will do you an off-peak single to Sunderland for £49, which you can buy on the train, on the day of travel, or an £84 return, which again requires no booking. They also often have sales or offers with cheaper fares. They don't do advance tickets, but rumour has it that they might be starting. Anyway, it's another option if you have to/need to travel but can't book. Note that they only run 4 trains a day in each direction, and only three on which you can travel off-peak.