Howdy,
For me, I use a local store for service, cheap consumables, impulse buys, and emergency needs. Oh, and skates, but I don't think its realistic that a small shop could compete here in any way other than as a custom order/fitter place that doesn't need to have any inventory.
For service... I think you have to offer (good) sharpening. Sparx has taken that need away for me, but that's not the norm for folks and I don't imagine it will be any time soon. What I can't do myself is repair stuff or higher end services like profiling. So, being able to do rivet replacement, holder swaps, etc. etc. Don't ignore figure skaters here... They need skate work too. :-)
Cheap consumables... Tape / laces / wax / water bottles (branded to you!) Pick a brand (Howie's?), buy enough that you get it cheap. And again... Figure skaters. Surely they have inexpensive stuff they need to replace regularly?
Impulse buys... For me, this is the general "cool shit that costs under $30 or so" kinda thing. Fun t-shirts (pick a couple designs targeting your rink residents. Do it in small batches, do new designs. Brand with your logo somewhere). Tape Tiger tools. Sweet Stick emergency sharpener tools. Lace tighteners. Water bottles with your brand. De-stinkify sprays. anti-fog sprays, etc.
Emergency needs... Skate steel in common sizes / types. Cheap jerseys in common sizes in a range of colors (buy closeout Tron or ebay stuff for crazy cheap?). Cheap socks. A small selection of basic sticks. Small selection of protective (jocks, elbows/shins, helmet, etc.). Your goal with this is more to have something someone can make work for the "Fuck, I left my XXX at home and I'm here for a game". Cheap (for you and the buyer both) is key. Its not going to move fast. Buy closeout Tron stuff when it comes available.
Other thoughts...
A used shop is an interesting idea. Either in consignment form or as a play it again sports type of approach where you own the stuff, but take trades in, etc. If you do this, then you can also fill your emergency role out this way, vs. buying new equipment.
Sell coffee / long term storage snacks. I can't count the # of times I've taken my son to a morning practice and forgotten my damn coffee. :-) And kids like candy. Dragging mom/dad into your small shop so they can get that $1 piece of sugary goodness as an "after hockey" habit is a great way for them to see that perfect t-shirt for grandma... :-)
Match your hours to when people will be there. If your rink sees a lot of adult league stuff, opening at noon on weekdays is kinda pointless for that market. Make your hours 4pm to 10pm or whatever.
Be the "if you need jerseys, I know how to make that happen" guy / team order of sticks / whatever guy. No clue on if there's any margin / profit area here though?
All just my "I've never been there or done that" thoughts. :-) If it were me doing this, I'd be talking privately with guys like JR, Buzz, etc. :-)
Mark