Kinem, assuming that I do approve the handy haversack (which isn't a guarantee), your carrying capacity would be 7.5 lbs which leaves you with 2.5 lbs of excess carrying capacity. If you are carrying anything more than that when your Str gets reduced to 1, you would fall over helpless, the sheer weight of what you are carrying pinning you to the ground. I'd probably let you roll an Escape Artist check to squirm out, but it isn't as simple as you seem to think. I'm just making you aware of the consequences of putting your lowest score into Str AND picking a race with a Str penalty.
Airwalkrr, you're the DM and it's up to you to make that ruling, but that's certainly not how I interpret the RAW. A character can stagger around with up to double his max heavy load. If falling prone were intended to be a risk of RoE I think it would have said so, though I can see it as a reasonable house rule from a flavor standpoint. As for being pinned though I just don't see it. If I weigh 43 lb and can walk around with an additional 7.5 lb, then a 2 lb crossbow is going to pin me down and I have to roll escape artist just to cast it aside?
In any case, I initially made a mistake on my light load capacity - it's 9.75 lb, not 12.75 lb. As a result I have ditched the crossbow and taken acid splash as a cantrip instead. With the items I requested that puts my weight carried at just 7 lb, which also happens to be under the max heavy load for a small Str 1 character.
There's very little that a sorcerer needs to carry. Going cross-country I'd do fine with just a pound each of food, water and cash. Once we establish a base of operations, for a day trip I won't even need those. I don't need a weapon, armor, or even a spellbook.
The haversack is for flavor mostly - it's something the character would certainly like to have. Without it I'd ditch the alchemical stuff. The other magic items could be useful in the right situations but only the cloak of resistance would boost my basic combat ability, and the slippers could be a big help in evading foes. If I don't get them I might try to rearrange my spells to include Spider Climb, though that would mean I'd have fewer options to aid the rest of the party while protecting myself.
The real danger of low Str isn't RoE, it's grappling. I have changed my final feat to Still Spell to help mitigate problems with that.
BTW, so when do we find out what items we'll get?