If your aim is to supply almost every town with food, I think it is good to use trucks. Usually I try to find a food processing plant above the snowline, supply it with lots of grain and livestock, and then distribute the food to nearby towns. Or if those towns are further away, it may be a good idea to set up a feeder service
by building a train station above the snowline, transporting the food there and then picking it up and transporting it to the towns by trucks.2.
Monorails don't become obsolete, at least if you're playing with the default vehicle set. The default monorail engines are available indefinitely.3.
If you provide good service to industries, their production will increase on the long run. See http://wiki.openttd.org/Game_mechanics#Industry_production
Thanks for your reply.
1. Okay, that is pretty much what I've been doing, but I haven't noticed a lot of results. Is there anything else I could transport besides food and passengers to help with population growth?
3. Yes I read that page. While I'll admit I don't have that many good ratings (as it seems hard to keep a rating up with without providing a lot more transport supply than you need, causing your trains to wait for cargo), my main concern is that as passenger trains can pick up cargo both ways, that freight trains basically have to make twice as much money in one trip as a passenger train does, and I don't seem to notice that at the current value of the cargoes. Thus if I had a limitless supply of say coal and passengers the passengers would still be more profitable due to them getting picked up at both stations, while the freight train needs to return empty.