If you train then you must refuel afterwards. I used to just drink water after a ride along with a sandwich but the next day my legs hurt. I was ok when I got on the bike but I would have an ache still. I always thought it was lactic acid built up overnight when I slept. How wrong I was!
I now use For Goodness Shakes. They cost about £1.20 each but I've currently found them at ASDA for 95p. They are also running a deal. Buy 2 for £1.50.
Northumbria University has recently conducted some research into them and it confirms that products containing protein aid recovery better than water or carbs alone.
From my own experience I find that they do work. I don't ache anywhere near how I used to the following day and the cost I don't find excessive as I spend more on my lunchtime sandwich than one of these. They have a long shelf life so you can stock up with these and they are also quite filling. Four flavours available, Chocolate which is very thick and some people could find sickly, superberry, my favourite, banana which is very nice and organic vanilla, which whilst nice it does leave an aftertaste and is also more expensive than the others. Probably because it is organic. They are good though.