Making a clamp used to be a huge affair for my dad - straw base, mound of root veg, mound of straw, earth mounded over that, holes filled with straw to allow the stack to breathe.
What's the objective?
A few veg when you want them, kept away from meece and frost.
Something that's easy to dive into when you want your veg.
The clamp is where veg can snooze all winter, cool or cold, slightly moist and kept in the dark ;D
A few rules - don't let the veg touch, make sure there's a mouse-proof layer around the clamp (my dad built a moat round his clamp one year :-X), and aim for enough insulation to prevent frost penetrating.
Alternatives?
Trench clamp - for veg that stand well in the ground - a temporary holding place on the plot so you can harvest even in a hard frost. Ideal for leeks, parsnip, JAs etc. Dig a shallow trench, put the veg in, and cover them with loose soil so you can see the tops sticking out.
Straw bale clamp - holds lots of veg that don't stand well in the ground e.g. carrot, beet, spuds, but will also hold any root veg. Easy to get to the veg, and the cover makes sure that meeces don't get in. Traditionally sand is used for keeping, but I prefer slightly moist lighter stuff.
Flower pot clamp - holds same veg, depending on size of your flower pot. Keep in cold greenhouse to protect from frost. Portable. Sand is too heavy for me although it's traditional.
Really keen to see how other peeps do it! ;D
