Fenris have a few bits that are worth considering including this cart. £5, comes without beast of burden but worth it still if you ask me. Talking of beasts, Fenris have some as do . . . .
Forlorn Hope Games have Oxen:
£3 each for 1 - 3 or £2.40 for 4 or more. I believe they have a mule of burden out soon as well.
I have just started a little baggage train of my own starting with a handfull of laden donkeys from TAG miniatures:
£6.50 for three.
You also Renedra who make barrels, saxon tents amongst other bits and bobs you may like.
http://www.renedra.co.uk/productlist.php?showall=0&perpage=48