Make sure any holes in toys are either big enough for a pig to fit in comfortably, or small enough that they can't get stuck in it. Use small animal specific toys, as dog/cat/child toys are often not made of suitable materials or contain harmful substances! Ensure any branches you give a piggy are not treated with pesticides etc, or collected from roadsides.
If you're not feeling creative then you can always buy some toys - there are so many to choose from including puzzle toys to stuff with food, treat dispensing balls, toys to chew on and cuddly ones to snuggle with - why not take a look online or try your local pet shop? Pet stores generally have a great range of small furry toys to buy, or even to inspire you to make your own! Most places have a range of prices to suit all.
Guinea pigs don't need expensive toys to be happy. Try simply stuffing a loo roll tube (obviously minus the loo roll itself!) with hay, and poke small chunks of their favourite veggies in for them to find. They can bite and rip the tube apart or pull out the pieces from inside! Mix different kinds of hay togther for a different flavour each time! You can do the same with a brown paper bag too.
If you have un-treated fruit trees in your garden, you can give sticks from them to your pigs to chew! Apple, pear, hazelnut and willow are some examples of safe wood for your pigs. You can usually buy these sticks in pet shops as well.
Simply scattering your guinea's fruit and veg around their home, and even some of their nuggets can provide them with an opportunity to use their natural foraging instincts. Try under hay, in their hideys or poked into the bars of their cage!
Enrichment doesn't have to mean toys. Spend some time getting to know your pig - get down on their level and watch them, see what their personality is like. Hold them, or if they don't like that yet, get them used to your hands by hand feeding them. Groom them and talk to them. Even better, find them a guinea pig companion to play with - see the 'Bonding' care guide for more info!