How could I make homemade handheld reflectors for portrait photography?

I have heard about using handheld reflectors with portrait photography outside. How could I make these, and what sort of size and shape should they be?

Making reflectors is pretty easy to do. Just use some aluminum foil (slightly crinkled) and tape it to a piece of foam core poster board.
Or you can use fancier shiny foil from art supply store, gold is nice to use for portraits because it gives skin a nice glow.
Another way to do it is to use one of those silver car sunshades from auto store.
As for size and shape, I always just made square ones, the ones I've seen in store though were usually round, prob not much harder to make round I guess. Size will depend on type of photos- closer in portraits maybe a foot and a half across, for full lenth portrait maybe use like 24" poster board or something?

actually white foam core works pretty well for that.

Basically anything white will work, or reflective for that matter. I've heard of tin foil over cardbord for that silvery look. The biggest drawback is that if your trying to be a pro, people wont take you seriously.

Spray paint on cardboard
Styrofoam
Cardstock
An old film projector screen
Just look around, you will find something

any large board or card
paint it white (brilliant white emulsion)

Lastolite 'type' are easy to move. Go for a decent size, 4/5ft wide, one side white.