"When I bill my clients I record these items as "reimbursable" expenses and understand this is "income""

The Expense is whatever you Bought and paid for: Meals, Travel, Office Supplies, Postage, etc; Even though you intend to Charge that to the customer = Selling it to them, to be Reimbursed, that doesn't change the Details for what you incurred.

"reimbursements may in some cases overstate your income - particularly for Meals.  For eg. if I have $3000 peryear in reimburseable meals, IRS let's me deduct 50% i.e. $1500 but I get $3000 back from the client. So now I have $1500 in additional taxable income when its really not income."

No. That isn't Overstating anything.

We seem to be confusing Gross and Net.

Gross = what you incur, in full; and what you are Paid by others, in Full.

Net = the difference. If I pay $500 for Stamps for you, and charge that to you, I have $500 Postage Expense and $500 Income to report. I have a Net of 0.

And the tax regulations and provisions have Nothing to do with this tracking. You track it, because you Need it for reporting. You report it, based on what the Tax regulations allow.

So, yes, you incur a $100 meal, and the IRS only allows you to take 50% as Expense, because we all need to eat, so that is not all Business. Meanwhile, you "sell" it to the customer for $100.

Yes, you just made $50 in Taxable Income, in that part of the expense is Not Reportable.

That isn't an overstated condition. That is Reality.