Measure your real daily carry
Lay out the items you carry every day and measure the largest one. Add a small margin for easy access, but avoid buying much more capacity than you need. Check the bag's usable interior dimensions, not just the exterior width; curved sides, dividers and closures reduce capacity.
Try the carrying position
Check handle drop over your shoulder and with a coat, strap length for crossbody wear, and how the bag sits when you walk. A bag that is comfortable in a boutique may feel different when loaded. If possible, fill it with similar-weight items and carry it for several minutes.
Balance size with weight and security
Ask for the empty weight and consider how the bag's hardware, chain and leather affect it. Check whether the closure is practical in public transport or crowded areas. For travel, consider hands-free options, a secure top closure and whether the bag fits comfortably under a seat.
Choose the use case before the trend
A small evening bag and a work tote solve different problems. If you want one versatile bag, test it against your commute, climate, wardrobe and storage space. The most useful size is the one that carries what you need without becoming burdensome.