How do you replace airplanes and cars? They both rely on fossil fuel.
Cars are pretty easy. Vehicles on the road are replaced fairly often (the average vehicle is less than 11 years old). We already have electric vehicles. It may very well be possible that we can keep our car-centric lifestyle by transitioning over to electric.
But there are other alternatives - we could rely more on mass transit, or even on using the existing vehicles more efficiently. Most trips take place with less than two people. Through carpooling and preplanning our trips, we could increase the amount of people transported on same amount of gasoline, no additional technology needed.
For planes, we can reduce our travel (less vacations in distant lands, more teleconferencing for business, etc). We can also use alternatives, such as rail (maybe we'll finally get a working high-speed rail system in this country!). And, of course, since "peak" oil means that we'll still have some oil even after the peak, some people will probably just pay the increased fares.
I'd even argue Peak Water could be a problem before Peak Oil. Water can't possibly be replaced so in that regard it may be an even bigger problem. So many potential problems in the future. If we're able to deal with a few of them, another one may come along that we can't replace. Every problem goes back to too many humans in the world.
Water is unlike oil that it is a renewable resource. Sure, we can pump aquifers that won't replenish in our lifetime, or destroy ecosystems to the point where desertification occurs, but a lot of the water we use is from resources that will be here today and tomorrow.
And what are we using that water for? We use perfectly drinkable water to keep our lawns green. We use drinkable water to flush down our urine and feces in toilets. We use drinkable water to grow food in arid regions to feed to animals that we (well, others) later eat, resulting in a massive loss of efficiency. We use drinkable water to grow food that requires a lot of water for human consumption, instead of growing crops that need less water.
When it comes to "peak", we're like spoiled rich people buying clothes we only wear a few times (if at all), buying the latest expensive gadgets for our homes, going out each night to expensive restaurants and clubs, and then predicting doom and gloom because our income is going to decrease and we have no idea how we'll survive.
