Remember you don't have to have the latest flavour-of-the-month boilies to catch carp.
For starters there's the Simple Stuff... worms, maggots, bread, etc., that will always catch fish, don't underrate them - when everyone's throwing in boilies, a big juicy lob worm may be just what the carp are looking for!
Your local tackle dealer is the place to go for all the ready-made boilies, mixes, flavours, colours, etc., etc., but a visit to the Supermarket and other local shops may get you a 'different' carp bait - that could give you the edge...
And don't forget that carp feed off-the-top in the warmer months - so have some floaters ready.

Simple Stuff.

Lets start at the beginning and have a look at what's on offer.

Worms - not many fish can resist a nice juicy worm or two, these little critters are packed full of amino acids, proteins, etc., they are easily available, pretty cheap to buy (even cheaper if you've got a wormery) and they do catch fish.
Inject air into one and you've got yourself a slow sinking bait, that attractively wriggles and twists as it falls through the water. Chop a few up and mix with bread crumbs and you got yourself a great groundbait.
If you are feeling adventurous, try liquidising them in a food processor - the resulting liquid can be added to your groundbait, or if you are pole fishing and have a steady enough hand, cupped straight into your swim.
Free-lined, method/feeder or float fished, the worm is a great bait, the only problem is, all the other fish think so too, so you will catch tench, bream, roach, perch, etc.

Maggots & Casters - There's not many fish that won't scoff a maggot or caster - and carp are no exception.
Fish a bunch of maggots over a bed of brown crumb and dead maggots - you'll get bites!
The best way to kill maggots is to put them in a polythene bag, squeeze the air out and seal tightly, then pop them in the freezer.
The advantage of using dead maggots is that they don't burrow into the silt, so they remain highly visible to any passing fish. Again flavours can be added.

Bread - probably more carp have been caught using bread than any other bait. Cheap to buy - bread can be used in a variety of ways.

Floating Crust - when the carp are feeding on the surface in summer, a floating crust is a sure way of gaining their interest. If you think the carp have 'wised up' to the crust - try colouring the bread with food colouring or even add a flavour to it, dip it in custard powder, smear a little honey on it, anything to make it different to fool the wiser carp. The addition of a drop of trout pellet oil works wonders.

Bread Flake - fished on the drop under a waggler or from a pole is a great bait, again you can flavour/colour it as necessary. A slow sinking piece of flake, gently disintegrating as it falls through the water is irresistible to most fish.

Paste - again flavoured or coloured, paste is a great alternative bait.
Try this: get a fresh slice of white bread (go for one of the cheaper brands, as these tend to be a bit more pliable), cut the crusts off, then lightly smear with cod liver oil (available from any chemist or health food shop), then knead the bread with your fingers until it turns into a pliable paste.
Another method is to put a few slices of bread (no crusts) in a clean cloth, damp the bread with water, (add any flavours or colours) wrap the bread up in the cloth, then squeeze and knead it until it turns into a smooth paste. If you put the cloth containing the bread paste into boiling water for a few minutes - it makes the paste even more sticky.
Try these flavours in your bread paste: grated cheese, fish oils, garlic (the pureed stuff sold in tubes at supermarkets), or aniseed oil, don't be frightened to experiment - what have you got to lose?

Cheese - This is a versatile bait that is often overlooked nowadays. A half inch cube of Edam on a hair rig, has caught me lots of carp. Try making a paste out of the more smelly varieties of cheeses.

Meats - Good old Luncheon Meat has been used to catch carp for years - and it's still catching fish today. It's got a lot going for it - it's cheap, full of flavour and protein, and it stays on the hook reasonable well. But there are better types of meat now available.
The best tinned meat I've found is Bacon Grill, it seems to have a better, stronger taste and smell than ordinary luncheon meat.
The strongly flavoured German sausages and pepperoni both available from supermarkets, make ideal carp bait, they tend to be a little tougher - so they stay on the hook better.
The specialist tinned meat you can buy in fishing tackle shops is well worth a try - it has all the additives, enhancers and flavours cooked into it, the Boosted Meat variety has caught me a lot of carp.

Sweetcorn - Yes - carp are still caught on sweetcorn, the Jolly Green Giant has caught lots of carp in its time, but I prefer to flavour any sweetcorn I use. Try soaking it in black treacle to give it an edge, it's sticky but it works! If you use a lot of sweetcorn, buy the frozen supermarkets own brand, it's a lot cheaper.
The flavoured/coloured tinned sweetcorn sold by tackle shops is also very good, it seems to be tougher than ordinary corn, the tutti frutti is particularly successful.

Other baits to consider - Cat meat (now very popular, but it has been banned by some fisheries), chopped liver, chick peas, tares, tiger nuts, mussels, cockles, marshmallow floaters - don't be frightened to experiment with baits, give them a try!

Don't forget - that purpose-built carp poles have opened up a whole new world for the specialist angler, enabling him to use softer baits than normal. Have a look at them next time you are in a tackle shop.