I can only speak from my limited concurrent experience but I'm happy to share what I've gleamed. There was no official welcome pack but I did get a lot of friendly emails offering help from folks in the dept.
I have just recently came back from a spring break house hunting trip in the city I will be moving to this summer for my new position. While in town I made arrangements to meet with the Dept. Chair again (in a much more relaxed setting than the exit interview!). We talked about class assignments and he took me around to introduce me to the dept. staff who would be setting up my accounts, helping me get equipment, etc. We also talked about setting up my website, ordering equipment, prepping classes over the early summer months.
It sounds like if I want to do something I just need to start asking about how to do it. He gave me relevant contact info for the tech/web people and showed me some of the possible lab/office spaces. I think that even if I hadn't been there in person, we could have accomplished much of the same over the phone so I would suggest setting up a call.
On that same trip I also had a chance to meet up socially with a few members of the faculty one evening which was a great ice breaker and informal chance to ask more questions - such as does my new dept pay for regalia rentals? Yes! Then I won't be out $900 buying any this spring! I also asked about when they usually have their faculty meetings so that I can mentally plan around that time slot going forward and their IRB processes (because I'll need to transfer some from my current home university). Even if we hadn't met in person, I felt encouraged to email with the other junior faculty to ask about realtors, preferred neighborhoods, quirks of commuting, etc.
I also just recently got an email about the formal college new faculty orientation (the week before classes start) but it sounds like that won't be all that informative. Instead the important piece will be getting an email account set up early so you're in the loop. If you want to get paid this summer I would suggest bringing that up sooner rather than later because it will impact your start date and will accelerate all of your other start up activities (like benefits!) but other things are less tied to your employment status (like a websites and email addresses).
I know with the accounts, they're going to be setting up one of my accounts in the next few weeks (to cover moving expenses) but others (lab equip) can't be opened until the new fiscal year (July 1st) so I'll have to wait until then to place orders. This may be particular to the university so I'd go ahead and ask.
Good luck and have fun!