I'm going to take the contrary view here and say that you don't need credit! I'm 27 now, and recently my credit score has gone to "unable to calculate" because I don't have one anymore (I had some credit & store cards and student loans when I was younger). Like you, I don't want to deal with credit card companies on principle... and I don't like the idea that I'm only valuable if I constantly get myself into debt. To address a couple of topics...
1) Rental cars. I've rented cars a couple times without a credit card. Usually if you're willing to put down a bigger deposit, this isn't a problem.
2) Mortgages. There is such a a thing as 'manual underwriting' which doesn't require a credit score... harder to find, but it exists. Anyway, I plan to buy a house in cash or not at all, as I don't believe in having debt.
3) Insurance, etc... maybe this is an issue? I guess you could be charged higher rates, but I haven't had any trouble with getting good, cheap car insurance so far.
4) Rewards -- the hassle of dealing with sneaky companies is, IMO, way more trouble than it's worth for rewards. Between my husband and I, we didn't have a single card that didn't either add some kind of 'identity protection service' charge, get the number stolen by someone, or screw up our on time payment at least once, so that we had to pay interest. The companies are scumbags, and it's not worth the frustration to 'stick it to them' by getting a few rewards. I use my debit card, where the account gives me 2% APY on the account balance, and for a while I had another rewards debit card (2% on purchases). There are other ways to get rewards without dealing with the sneaky CC companies.
If you want to deal with a lot of hassle and play by other people's rules, get credit. Me, I prefer just having money.