There are bags for all occasions, but I am a firm believer that you should have at least one good quality bag that is timeless and goes with everything. If you are making an investment, then you really want it to last a while.
Check how the handles are secured. Handles that are well stitched will last much longer than those that are attached just at the edge. Even better are handles which are stitched part way down the bag or even all the way underneath. I have been a victim of broken bag handles, which are not ideal at all and you end up with the contents of your bag on the pavement for all to see.
Pockets and compartments are good. Looking for your keys amongst loose items in one large compartment can be a nightmare. Things like keys, and train tickets should be easy to access. Valuable items should be zipped away for security. Women are known to carry all manner of things in their bag and a little organisation can be extremely useful.
Avoid beading, and fussy details. These are likely to fall off or get damaged fairly easily and will make your bag look shabby far sooner than it should. Also remember that you will be carrying it under your arm, and anything bulky or sharp is going to make carrying the bag uncomfortable and can leave your arm covered in scratches.
Leather Plaited Handle Shopper - ASOS - £60
Carry a cotton tote. It takes up hardly any space in your bag but means that if you pop to the shops you can avoid taking a plastic bag, and yours will be stronger and more stylish to boot. You can pick these up almost anywhere at the moment, I carry a 'frock me fashion' tote, a bargain at just £3 including postage.
Be minimalistic. If you change your bag from day to day then it is good to have something to empty the contents into at home, like a little basket. This avoids missing needed items out when you swap to a new bag in a rush the next morning. It also helps to de-clutter. It's a great wonder the type of random things that get collected along our travels and homed inside our bags for evermore. Reminding yourself to review the contents can be a good exercise.
Good luck shopping, I hope you 'bag a bargain'
BAG - Alphabet Tote Bags
BAG - Eel Skin Clutch by Makk
WANTED - Chloe Turquoise bag