Bitcoin Forum

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?

There are Android wallets that have "buy" features built in... but a lot of them include massive mark-ups/commissions... Mycelium for instance uses "Simplex" and allows you to buy with a credit card, but has something like a 10% fee! :o Also, it is BTC only... no ETH or LTC support.

Coinomi has support for multiple coins... and conversion between coins with ShapeShift/Changelly etc, but I'm not sure it has any facilities for actually buying coins.

You're possibly better off just using a "traditional" exchange like Coinbase etc to purchase coins, and transfer them to your mobile wallet as required.

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.