Nope it's not a decent chunk of people at all. Here is an estimate of the itemizers. As you can see it's an estimate of 13.7% that now itemize and of that 13.7% over half comes from the top 10%.

Sales tax on a large purchase? Yes it can be deductible but most people would deduct their state income taxes paid instead so that's an almost moot point. Charitable deductions, again are deductible but under the new law they have gone down and most people can't or don't donate anywhere near close enough to make worthwhile to maintain receipt records.

Medical expenses again are deductible but it's more complicated than you're making it. There is a 10% AGI floor on medical expenses. I.e. you must reduce your medical expenses by 10% of your AGI to even get them on your schedule A. You also can't have an HSA pay for the expenses you want to deduct since the HSA money is generally tax-exempt income.

I'm not sure what you're getting after with dependents since you don't get a deduction for dependents. There is a childcare credit but it doesn't factor in your itemized deductions bucket.