Wilderness Exchange is within walking distance of Union and they require you leave a bag with them when you go into the store, they may be willing to stash your bag for a few hours. No guarantee on that, but an option if you can't find anything else. They are only open 10am-6pm on Sundays, so you may have to wait around a bit or pick it up early depending on when you get there and will be leaving.
Once the Union Station redevelopment is complete, these buses will have a pristine, new hub—underneath 17th Street between the historic Union Station and the Light Rail Plaza. This beautiful underground bus terminal will accommodate 22 bus bays for easy, congestion-free transfers. There’s also an underground, enclosed passenger concourse so you can get where you’re going easily and comfortably.
Locking options: various types of key locking or padlocking facility are available now. Key locking options include flush locks, cam locks, or locks incorporated into a rotating handle; padlocking facilities may be a simple hasp and staple, or else a padlocking hole may be included in a handle, often called a latchlock. More modern designs include keyless operation, either by coin deposit (which may or may not be returned when use of the locker terminates), or by using electronic keypads to enter passwords for later reopening the locker. Some older lockers used a drop-latch which was incorporated into the door handle, and slid up and down and could be padlocked at the bottom in the "down" position, but these are less used now. Three-point locking is not possible with this type of latch, because it needs to be operated by means of a latch that rotates rather than slides up and down; so this drop-latch is probably a less secure locking option, which may be why it is little used nowadays. Prefect Combination locks are very popular in school lockers used in the UK due to their ease of use and the time and cost saved in the removal of locker keys.