Is there an Android wallet, that allows for quick and easy BTC/LTC/ETH transfers (like to pay a merchant at point of sale); but also has a menu to let you top-up your balance and buy more crypto?
Coinbase is the best ever wallet with exchange you can buy BTC,BCH,LTC and ETH in coinbase exchange but it is not available in all the countries so check the official webiste of coinbase to know about that features are available or not in your country.
Blockchain.info wallet also comes with builtin exchange where you can buy bitcoin and ETH only but I never tested this feature yet.
Yeah coinbase is the best app where we can buy all the three coins that OP mentioned but blockchain.info wallet also has the built in exhange where BCH also added recently as coinbase but LTC is not added yet.
But OP need to be aware the Scam apps there are lots of scam apps are available in playstore so check the feedback before installing.