Hmm... IMHO I would say "no". I agree with TheCommuter re: pizza, furniture, newspaper, etc., but those are things you ASKED for them to bring to your house. The flowers were a gift from someone else, in which case it would seem strange to me that I would have to pay to accept a gift. Plus, if you're not expecting them how would you know to be prepared to have the right amount of cash on hand? (I tend to not carry much cash on me unless I know I need it).
I tip anyone who comes to my door (to bring me stuff) under the following circumstances:
I have a couple bucks on me. If I wasn't expecting them, I'm not going to make them wait while I hunt around for singles.
They aren't creepy. We have grocery delivery here in NY (FreshDirect) and I had to stop ordering from them bc the guy for my area (and it was always the same guy) was reeeeeally creepy. Like, he'd make comments on decorating changes I'd made to my apt since the last time he was there. I'm a young, small woman living alone. You do not get to come to my house anymore, creepy guy!