I see plenty of people saying that they routinely remove it from the account "just in case", so your perspective is refreshingly different. I don't think you can ever have "excess cash", myself, to be honest ... but I suppose I know what you mean. I've been known to buy old musical instruments (not terribly expensive ones) and vintage wines. Decent string instruments seem fairly reliably to appreciate in value three-fold every 7-8 years, but you definitely need good advice about what to buy.
If you're UK, spare cash can go into Premium Bonds - government guaranteed, prizes equivalent to savings interest rate p.a., which is not fantastic, but there's a chance to become a millionaire each month.
We recently sold our home, and decided to rent. I set up ladders for my wife and I using Treasury Direct. One Ladder rotates a set amount of Cash in 13 week Bills. So every week a Bill Matures and gets re-invested on a 3 month cycle (13 separate Bills). The other Ladder rotates an amount roughly equal to the 13 week ladder. Except here it is designed to roll short term Notes. It was created in a fashion so as to "leg in" to having 3 Year Notes rotating each month. To create the "leg in", I started by Buying 13W, 26W, 52W, and 2Y instruments. By the end of the third month the Cash was cycling itself. In this fashion, if I suddenly need a sizable amount quickly I will have availability to the 13 Week Ladder each week for 3 months. Then of course a monthly inflow for three years. My wife has a similar account, so if one of us passes away suddenly the other has access to funds until everything gets sorted out.
I use savings accounts. As of today 4-28-18 rates are Synchrony Bank 1.55% American Express Bank 1.55% Barclays Bank 1.50% Discover Bank 1.50% Ally Bank 1.45%
Works as advertised. Pays 1.6% these days. I've had no problems shuffling money in and out, but there's a limit on the number of transactions. Also they have (or had) a maximum account balance, I think $300k. If you're a heavy hitter this might be too little to be worth the bother.
Lately I've been laddering T-bills. I bought a chunk at today's auction. They yield more than Marcus or similar accounts, and the yield is free of state tax.