Yeah, basic idea is not alter course itself anyway but can alter yourself (with limitation of no flying and teleportation). You could go ant-man style to avoid the sacks example as they do not hit the floor of the area (but going flat and crawl would not help even small humanoid in there and speed would reduced anyways so it does not help). So there's room some creative spell uses. Also conjuration is allowed (so long anything conjured does not allow teleport or flying). Also magic items (with activated effects than passive buffs like cloak of resistance or bracers of armor) are not allowed so that further limits things.