Thanks for your two-sided view regarding my question!

I'm still thinking about it, since it would take a bit of time to digitize the whole work...
So, finally, I've finished my item hunting!
And I'm absolutely sure, that I fullfilled the description of the Collector accolade literally.
I collected a total of 451 items, had to kill 244 enemies to explore everything, looked at the maps 941 times, walked 128,72 km (that huge distance resulted mainly in checking walls) and had a playing time of 88:48:24.
Like I said, I completed the game almost without using healing items or Energy Drinks at all - only two First Aid Kits (I still need to improve myself on the penultimate boss

) - in order to eliminate the healing-item-spawning-feature I heard of, so that only the standard items would appear.
I compared my own run with those of three other famous walkthroughs found on GameFAQs.
The biggest item differences I've noticed were with a comparison of my run with a mapthrough whose author I believe must have used many healing items during his playthrough, because especially at the Hospital and the Sanitarium stage he had found several times Health Drinks instead of Energy Drinks, Energy Drinks instead of nothing, and later in the game First Aid Kits instead of ammo.
The other two walkthroughs however almost always list the same items I've found. The only differences were at the Sanitarium stage, which I believe is down to the fact that players normally don't arrive there without having used a healing item or a melee weapon, and because of the relative small inventory at this early point of the game. That's why I made sure to arrive at the Sanitarium without having used anything, to keep my inventory at its maximum. During the stage, I searched unsuccessfully for two Health Drinks, two Energy Drinks, and one Meat Hook that one or both of the walkthroughs list.
But at all the other places I've found the same as them - only one Hammer in the last normal Streets section was missing at my run.
Those maybe could also be PS2-PSP-differences.
Now to the item number comparison: I've found about 30 items more than the mapthrough (don't know if on PS2 or PSP), and about 10 items more than the walkthrough that lists the highest item number (on PSP); with the third walkthrough (don't know if on PS2 or PSP) I haven't compared my results in detail, but there were also many missing items I've found, like with the first one.
To cut a long story short, I'm pretty sure that 451 is the highest number of standard items achieveable on a 1st time playthrough!
And on a side note, what I also found out during this run: Unlike in some other SH games, Travis turns his head at every single collectable item - outside of buildings at about twice as much the distance than inside a building (but unfortunately, a couple of times also at things that aren't of any interest).
Like I said above, I don't know if I will ever digitize it (depends on mind, time and demand), but in the next days, I'll post a statistic in any case - for those interested in how many items of each type the game contains.
