I used to grab the 23 to Asda when I lived down Plungington Rd. Doesn't take long to get there, n it's never usually too full (just don't get it at rush hour, it gets stuck in all the traffic and takes about an hour to get back.. Erk!).
As someone said, it costs £1.10 each way, so £2.20 for the total journey. However, if you can grab three friends who all also wanna go shopping, you can purchase one of the not-advertised 'Family Tickets' (just ask for a 'Group Ticket'). These tickets are for groups of up to 4 people, and permit you one return journey between where you get on and your destination. So you can save yourself a quid or so doing it this way.. Every penny counts, eh?
As for fresh produce, there's always the Preston market. I know people don't seem particularly enthused about buying things from markets these days, but the quality of the produce down there's great and often works out cheaper / the same price. There's also a butchers down Plungington Rd who sells great bacon, yum.
There's also two Icelands in Preston. One of them is down in the centre, and one of them is behind Moor Lane Halls. The one behind the Halls is just as big (if not bigger) as the one in town, and often not very busy. The prices are just the same, and it's actually nearer for most people to go there than to trek into the town centre.
Hope this helps..
Shoe.