Prop ideas
This is a page to list props and their uses, including mundane items which often come in handy (like ribbons), and items which are less well known but could prove useful in putting together a game (such as new toys).
See Prop suppliers for detailed advice on specific suppliers.
Hats
If you're trying to establish the moderator as some sort of authority figure, you can't really go wrong with a good hat.
Beret = artist/secret agent, bowler = businessman, top hat = toff...
Magic pens
UV pens have ink which is only visible under UV light. They are probably available free from your local law enforcers (for marking your property to aid recovery if it is stolen). You can get UV or 'blacklight' lightbulbs, torches (used for examining stamps or currency), and LED keyring dealies - these are available at electronics/hobby stores.
Secret agent pens are toy sets of two pens, one which writes invisibly, and one which makes the writing from the first pen visible when you scribble over the invisible message. Usefully, the ink in the invisible pen may also be revealed under UV light.
Also see Lemon juice secret writing.
Mobile phones
Very basic pre-pay mobile phones are surprisingly cheap nowadays - you can pick them up for £20, or even less with a mandatory credit top-up. Smaller, dodgier stores will sell you unlocked handsets so you can replace the SIM.
In my experience, trying to save money by buying a second-hand mobile is more trouble than it's worth.
Ribbons
Looped ribbons are a cheap and easy way to denote teams.
Voice changers
There are voice changer toys shaped like loudhailers which both amplify and change your voice to give a Dalek/alien type effect (some of them offer a variety of effects).
You can also get smaller voice changers designed to be held over a telephone mouthpiece.