If you're attacked in the street it's unlikely you'll be fortunate enough to have a weapon with you. A nice baseball bat, for example, would be the ideal way to deal with two attackers, or a single knifeman. (If you're lucky enough - and aware enough - to see the knife before it's too late).
Unfortunately the police usually get upset if people walk around with a baseball bat, a fighting knife, or a knuckle duster. We, law-abiding citizens, are nice people. We go unarmed and avoid trouble. But unfortunately there are a few very bad people out there who would lose no sleep after biting off your girlfriend's ear as they grapple for her phone. Others would positively enjoy the experience of jumping on somebody's skull repeatedly, maybe until it splits and leaks brain onto the pavement. For no reason at all.
Fortunately, there are some opportunities to use common, everyday items that are usually legal to possess in a public place. Most of them aren't as effective as a baseball bat or a knife - but they're better than bare hands.
Umberella - a favourite because it's so legitimate to carry and because it's long. Don't swing it around, the edges are too soft. Use its length to your advantage. It's longer than a knife. Stab to attack the body's most vulnerable pressure points. Strike hard and strike repeatedly. The best thing about a long weapon like this is it makes it possible to keep your attacker at a distance.
Screwdriver - perhaps the next best thing to a knife! You can't usually go around carrying a screwdriver without good reason on a night out, but during the day you probably will, and it's fine to keep one in your car - for those mechanical emergencies requiring a particularly long and pointy screwdriver. In a less serious situation you might use the back of the screwdriver to strike the jaw and cheekbones - but don't rely on that in a kill-or-be-killed situation.
Pen - perhaps the next best thing to a screwdriver. Use it on the softest and most vulnerable targets.
Spray - spray cans are a useless weapon at anything but the closest range. But if he's already grabbed you and there's nothing else and you've got one in your handbag, obviously go for the eyes. It doesn't matter what it is. Try to find an aerosole that sprays a long way. Or a bottle of skin product that stings if it gets in your eye. Some of these have quite a long range. Cuticura anti-bacterial hand gel is good, with a potential squirt-range of several metres. (You might even want to refill the bottle with something a little more potent - do you enjoy chilli sauce on your food?)
Steering-wheel lock - did I say you're not allowed a baseball bat? This is the next best thing. You can even buy ones that are shaped like a baseball bat and nobody minds you having one in your car. (The car is a good place to keep your arsenal of legal weapons.)
Dog chain - if you haven't got a dog, get one, they're nice. And they give you a legitimate reason to carry a chain. Chains can be ferocious weapons, either for whipping the face at a distance or bunching up and striking the temples from closer up. As a last resort, use it to choke your attacker.
Newspaper - don't take my word for it - roll up your paper tightly and fold it over tightly too. It's as hard as a piece of wood. Ideal for striking vulnerable targets at close range.
Dirt - just scoop it up and throw it into the eyes. Fine, heavy grit or sand is ideal and you'll often find some on the floor. It's perfectly legal to carry around a small bag of sand - although it may initially be mistaken for something else. Even one small fragment of dust or grit in the eyes can be completely debilitating for a few vital seconds.
Use your imagination. You'll think of many more. Think maximum vulnerability and maximum damage.
When you're out and about get in the habit of identifying the items around you. Keep asking yourself, "somebody jumps me right now... what would I grab?"
It's a sad fact that people who respond to an attacker with a weapon often lose the weapon and have it used upon them. Don't be one of those statistics. Don't even think about having a weapon to hand unless you're 100% sure that:
1. You're prepared to do gruesome damage with it - without hesitation
2. You know where to strike on the attacker's body (see the self defence DVD)
3. You're familiar, comfortable and capable with your weapons.
Experiment - try waving a few things around, maybe striking a punchbag or other simulated attacker. Find out what feels best for you - and practice, practice, practice, until using your improvised weapon is second nature. As you practice, visualise the situation. Try to imagine the terror you'll feel - and the hesitation to hurt another human being. Strike swiftly and pull back. Don't let the attacker grab your weapon. If they get hold of it, try to keep hold but claw and poke their eyes with your fingers as a last resort.
Overcome your obstacles in training. In an ideal world, training would be harder than real life.
Train hard, fight easy.