I have up to 5% of my nestegg in cash in an online savings account.
Inflows are principally taxable account dividends and transfers from taxable accounts to replenish the fund as part of our annual rebalancing.
Outflows are transfers to a local credit union account that we use to pay our bills and occasional ATM withdrawals. Most of the aforementioned transfers are an automatic monthly transfer.... our monthly "paycheck".
The rest of the portfolio is 60% equities and 35% fixed income. When I rebalance I first sell taxable account equities as needed to bring the cash back up to 5%, then sell equities or fixed income and buy fixed income or equities as needed to rebalance in my tax-deferred accounts.