Asda have a pack of 6 crackers for £3, online and instore. They come with the hats, jokes, etc, all you need to do is add the gift!
This is my first post in years so apologies if it's not quite right or in the wrong section. I have noticed on this forum and others people asking about ideas for make your own crackers so I've included a few below.
Scratchcard/lottery tickets: You can buy festive themed scratchcards for £1 or £2 or pop in a lottery ticket for an upcoming draw. Another option is to include a betting slip (say for £1 or £2) on whether it will be a white Xmas or what will be Xmas number 1 etc.
Perfume: Lots of companies make miniatures of their perfumes and market them as purse/handbag sied. Perfect for crackers. This option is availble from Avon for £0.99p (inc delivery if you order online and select rep delivery) https://www.avon.uk.com/product/4678/far-away-infinity-purse-spray?cb=-1440600406
Another option is these sets of 3 perfumes from M&S. £5 for 3 perfumes. http://www.marksandspencer.com/eau-de-toilette-purse-spray-trio/p/p22478289?prevPage=srp
Cufflinks: Loads of cheap cufflinks available on eBay and Amazon. These Lego cufflinks are £1.75 inc postage from the UK. http://www.ebay.co.uk/itm/Lego-Cufflinks-in-Blue-Christmas-Birthday-Wedding-/282233482558?hash=item41b66d2d3e:g:nrAAAOSwHsRYEHx5
Jewellery: You can get some expensive earrings, rings, bracelets, charms etc or you can go for cheap and festive. This 3 pack of Xmas earrings from Asda is £1.75. http://direct.asda.com/george/womens/accessories/3-pack-christmas-drop-earrings/GEM318003,default,pd.html
Out of stock online but still had plenty in my local store so worth checking. Ebay has loads of options too. http://www.ebay.co.uk/itm/1-Pair-Christmas-Reindeer-Earrings-Red-Enamel-Leaping-SilverTone-Gift-Bag-or-Box-/252627330240?var=&hash=item3ad1c324c0:m:mSHPlrmM1rqngJFx_cRMYaQ
£1.69 inc delivery from the UK.
Make-up: If you know want brand someone likes you can get a nice nail varnish, mascara, lipstick etc. Revlon lipsticks currently on offer at Superdrug. See HUKD post for details. Cheaper options include 2 items for £4 at Avon https://www.avon.uk.com/special-offers/249/
Toiletries: You can easily fit miniature shower gels etc into crackers. Original Source miniatures available from £1.05 at Superdrug http://www.superdrug.com/Original-Source/Original-Source-Lemon-%26-Tea-Tree-Shower-50ml/p/98744
You could also go for miniature hand creams, moisturisers etc or pricier options such as Molton Brown etc.
Socks: Socks can be squeezed in as long as you roll them up tightly. I got a few pairs or festive socks from Poundstretcher for £1. Poundland also have options. These socks from Poundstretcher are £1 each or 3 pairs for £1.99. http://www.poundstretcher.co.uk/snuggle-socks?
Food and drink: You can put individually wrapped chocolates or sweets into the crackers. Lindor balls are always popular or Quality Street etc. Sachets of hot chocolate are another option. Alcoholic miniatures fit too. From £1.09 at Drink Supermarket http://www.drinksupermarket.com/miniature-spirits?dir=asc&order=price
Other ideas include a nice pen (Parker or similar), Swiss army knife, gift card and if it's a cracker you're making for someone you dislike, I suggest filling it with glitter. (Make sure you don't pull it with them!)