ontop of working out can i just supplement all of my meals with food supplement shakes and bars?
or would that kill my body?
That would
totally kill your body - that's why it says in bold lettering on the side of the shakes that they are
only intended to replace 1-2 meals per day.
It's simple maths: 3500 kcal = 1lb weight. You need to reduce your total weekly calorie intake by 500kcal per day to lose 1lb per week, and you can keep that up indefinitely (well, until you reach that goal). Be aware that undereating (e.g. a woman having fewer than 1200kcal per day, more like 1800 for a man) will cause your body to go into starvation mode, whereby it conserves all the energy it can and will just make you sick rather than skinny. A woman can healthily stick to 1500 kcal per day for months on end; a man can eat 2000 and be fine and still lose weight.
All (mainstream) diets are equally effective because they all involve putting less food into your mouth. If you have a plate of chicken and rice, and just eat the rice or just eat the chicken or have both but only eat half then you'll still be ingesting the same number of calories. Again, though, you can easily make yourself sick so having-both-but-having-half is your best option. As for shakes and meal replacement bars, try using them for one month (replacing breakfast and lunch) to get used to consuming less, and then reintroduce regular foods in smaller portions (swapping foods for their low-fat equivalents where applicable) - you're looking at approx 250 kcal per meal, which is one shake, or two slices of buttered toast with Marmite, or a big bowl of cereal with milk. In all cases, have a regular balanced evening meal of around 700 kcal and have a couple of 100-calorie snacks throughout the day - obviously fruit and veg are ideal, but a chocolate-topped cereal bar can be good to satisfy that junk food craving.
Edit: Also crisps are terrible for you. Make a sandwich or something, but don't just eat crisps and a chocolate bar and call it a day.
Crisps are unfairly maligned - they are, after all, just cooked potatoes. The important thing is to consider type and portion size. A big bag of McCoys has something like 250 kcal and a bucketload of fat and salt, whereas a small packet of Walkers regular has more like 120 kcal and only about 7g fat - comparable to the "diet" snacks you can buy in Boots. If you are a regular crisp-eater, stick to multipacks - each packet size is much smaller, nearer 25g where the shop-bought ones can be up to 50g, and
that's where you get unhealthy. Better get, go for the baked-not-fried varieties and look out for low-sodium flavours.