Fat, oils and grease can all solidify when they cool down. Many homeowners dispose of cooking fats in the sink, which is fine until it's time to wash up. The water mixes with the fragments of food still stuck to your plates or utensils, and without proper care can cause massive blockages.
As trees grow, their roots can find a way up the drains and cause blockages. This usually happens when the roots break into the pipes, allowing dirt and debris to make their way in and catching waste as it comes through, forming a blockage.
Food that hasn't been washed off before going into the drains can block them too. Food scraps or other types of food debris from cooking or dining can end up clogging the drain if they're big enough. Thankfully most sinks have some kind of filter these days, so the risk is low.
While they might be called disposable, you really shouldn't be flushing wet wipes down the drain. Disposable wipes don't break down well, instead getting caught in your drains and forming blockages over time. This effect is amplified if you're flushing other things as well, such as rubbish.