- Taste. Even food can be a prop if it's in keeping with the theme / mood. Tea and cucumber sandwiches provide a mood different from Mountain Dew and Salt & Vinegar crisps. Bonus points if you play an NPC and hand out the treats in game. It’s a great way to get the player’s to drop their guard and potentially partake of poisoned drink so long as you point out that what is drunk out of character is also drunk in character.
- Temperature. Environmental changes can also assist in connecting the players to the characters. However, don’t make it too uncomfortable and do allow your players the right of veto. At the very least, let them rug up if you turn up the air conditioner. They'll still get the point about how cold it is even if they experience it in relative comfort. Another thing you could do is keep a glass of icy water handy (preferably with a film of ice over the top) and dare them to plunge their fingers into it when their character dives into the icy water. Never force them to do it but feel free to offer a reward to those who do. Another option is to swap between a cold room and a warm room for when the players are braving the inclement weather or hiding inside. That can provide an excellent incentive if you want the characters cooped up inside!
- Sight. Pander to your player’s sense of sight by providing photographs of important NPCs, diary props, maps, and other physical clues rather than simply describing them. Don't forget to give them the time to read these props, though, and be aware that some players will want to painstakingly go over them (which might take awhile) and others will cast a cursory glance at them and move on.
- Smell. Baking cookies can lure them into a false sense of security (especially if coupled with a kindly old NPC lady and some candle light). Incense provides exoticism and may remind them of where they are as they walk into that cultist den. A lit match has a distinctive smell as does fresh leather or perfume sprayed on a card. Just be aware of your player’s limitations and be safe. Some chemicals in both food and containers are hazardous to smell. Also be aware of any asthma or scent allergies. Some people get head aches when they smell lavender oil after all.
- Touch. Bring touch to the fore with props your players can touch (i.e. fake cigars, diaries, flash lights, and weapons props). Just keep them out of reach of fiddlers! Some people learn better through touch and everyone remembers an object better than a description. This can also be utilised for in-game ramifications, such as the Keeper who handed his player a rusty flashlight that hadn't been quite screwed on tight enough for the batteries to power the light. The player immediately tightened the flashlight lit and it made an awful noise ... that drew down the Enemy. Which is great stuff.
If anyone's created any really awesome props, mention so in the comments below!