Because mums (and witches) go to Iceland

What you find around you can be used for magic as long as it has an effect on you: if it is quaint or picturesque and this helps you, more power to your wand. (Picture courtesy of TranKmasT on flickr)

To work magic it is not necessary to have access to incredibly exotic or expensive ingredients, unless you want access to a particular magical current that requires silver, lambskin and parchment. To work 'low' magic, of which the basic principle is that you can use your inner world to influence your outer world, it is much more important to use the materials that press the right buttons in both worlds. Of course it is possible to work magic in a completely mental manner, with no 'props' at all. However it took me ages to realise the purpose of the tables of correspondences you find in the magical books, that is, collections of things which have links to each other in the greater picture, and which can therefore be used to influence each other by manipulation of something in the smaller picture. Similarly I had difficulty understanding 'as above, so below,' but of course this is a seemingly more hierarchical way of expressing the same thing.
Similarly, because it is important that the materia magica make an impact on your inner world, this will be related to your personal hedge, the source of your personal magic. Different things mean different things to different people, however it is also notable how magical traditions adapt to their environment. Hoodoo (African American folk magic) is a prime example of this. African slaves transported to the Americas didn't have access to the plants they'd used in Africa, so began to use local plants for magic. As they came into contact with Native Americans, they integrated aspects of their folk magic, folk elements of Catholicism were also incorporated from their captors, and even elements of Kabbalah or Solomonic magic were incorporated from contact with Jewish pharmacists, whom white people didn't want serving them. Similarly modern witchcraft uses a greater paraphernalia of ritual equipment because of its availability. Our predecessors (that is, those who have always done what we do now, even though they wouldn't usually call themselves witches) used many fewer 'tranklements', and the props of magic do change with time.
For witches who live in urban areas, without access or understanding of the ancient herbs and weird substances prescribed by many of the books, our hedge is formed by the things we find around us each day, and these things can be turned into our own correspondences and used in magic.
For example I'm very fond of bottle spells because they are so adaptable and can be kept so that someone like me who tends to scratch can come back to it and have another go without bringing back the spell. Finding an object  link of the person is not as hard as it seems: people leave bits of themselves all over the place unwittingly. Once I have it I often speak to it, I usually keep it on the altar for some days until its identification with that purpose (person, intention, institution) is complete in my mind. I usually use large coffee jars, and will put the object link in it, doing this more or less ceremonially depending on my mood, remembering that the important bit is the total identification of the object link with the person in my mind. What I then do with it depends on the purpose of the spell. I will pour vinegar over it if I want to make things unpleasant for them, again because I hate vinegar myself, and I will visualise the unpleasantness happening to them. If I want to make it sweet I pour over runny honey. For them to have pangs of conscience I use nails. To stick someone in a situation of their own creation glue is wonderful...you get the idea.
A lemon can be used to embitter a person or thing. The hair from a cat and a dog can have marvellous effects in starting rows. I was astounded to discover that the ingredients in many Hot Foot Powder recipes are the same as the ingredients in chilli powder, so that's what I use. You can steep herbs in oil to make it for different purposes. To cleanse? Jolly old sage. In higher amounts this can also be used as Essence of Bend Over because it's so overpowering (and usually overdone in shop-bought stuffing). You get the idea.
Even if I can't get an object link I usually don't have any trouble creating one. I often use things bought from charity shops, just being careful that they remind me of the person or thing the spell is for. I have used a letterhead to cast a spell on an institution. I love what Dorothy Morrison has to say in her book Curses, Hexes and Other Unsavoury Notions about using Barbie dolls as poppets. She suggests ways of personalising them to the person. The only thing I've never been able to work is her idea of stuffing the doll's cavities with things for the spell, for example cotton wool in the head to induce confusion. Perhaps it's just that I don't take them off gently enough, but I can never get the bits bask on (they make a nice popping sound when you pull them apart, though). Nails are surprisingly difficult to get through them. I once nailed one to the bedroom floor without meaning to, using a mallet and masonry nails. I have bought china ornaments that have reminded me of the target of the spell. As a general rule, if I've thought about the spell for long enough, suddenly the materials for it will appear, the time will feel right, and the spell will almost do itself. Perhaps this explains why the effect of a spell is often noticed just before you've actually done the action: you've already made the necessary changes elsewhere and things are starting to fell into place. That said, when I once turned a pig's ear into my problem and fed it to a friend's dog who shat it out all over the house, it didn't take that much turning!